Tank Reboot & How to fix GHA problem

taulgrl

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I’m weeks away from moving my current 5 yr mixed reef to a new Waterbox 110Ex system. New tank and sump are about the same size as current tank (80 gal)

I have been battling uncontrollable GHA growth in my current tank for almost a year and nothing seems to be working. Parameters in line with recs and stable (Alk 8.5, Nitrate 5-10, Phos 0.03). Running GFO, carbon, and dose Kalk. I replaced all RODI cartridges and membrane, have ~30 snails, 2-3 urchins (big and old tuxedo just died), a few hermits and just got a sea hare (who doesn’t seem overly hungry). Algae eating fish = Scopas tang. Maintenance = manual GHA removal w 10-20% water change every week or two. It just grows back like crazy!

So, I’m giving up and hoping that moving to new tank will help. All equipment will be new. My plan: I’m starting w new live sand but I hate to start over w new rock. My plan is to scrub the heck out of them and rinse in fresh RODI before transferring.

What suggestions to people have? I’m wondering if I should throw my UV sterilizer in to see if it helps at all… only thing I can think of other than adding algae killing chemicals (don’t want to do that)
 
Last edited:
Good luck!

Personally I would scrub the rocks and rinse with tank water. That way your beneficial bacteria won't be impacted, and you won't have to worry about any die-off polluting the new water. You'll probably want to give them a good shake in the water too. They're likely full of detritus by now.

I'd add the UV, especially since you've retained a lot of your beneficial bacteria from scrubbing the rocks in tank water. I'd run a protein skimmer too if you have one.
 
Adding some or all live rock would be the first thing I would do. If you scrub the the existing rock (which I understand and don't disagree with) and rinse it in RODI its going to be very similar to starting over with dead rock and the same rock that's already proven to grow algae. Did you start with dry rock the first time? I know many succeed with dry rock start ups but when I did it my tank was a mess for over a year untill a seam failed and I broke the tank down. If I use dry rock in a display now I pack the sump full of as much live rock as I can fit and I've pretty much avoided any uglies. I don't know what causes it but I've had some rock get covered in GHA and the rocks around it remain algae free.
 
GHA is complicated, but not overly so. It's almost always a combination of three factors:

First, overloading nutrients into your rocks. The waterborne nutrient number is irrelevant here - GHA is a huge nutrient sink, so it's very common to have a tank with an overgrown GHA and low or non-existent testable nutrients. Detritus settles in on your rocks and serves as in in-situ source for algae growth.

Second, inadequate consumers. Algae is everywhere. It's always going to pop up. So you need things that will eat it when it does pop up. But, once algae gets too long, your critters become disinterested in it. Too hard to eat, doesn't taste good - I'm not an algae eater, I don't know why they don't like it. I just know that they don't. So once it gets really long, your algae consumers will skip over it in favor of other sources. But on top of that, it's not just algae consumers you need. You also need scavengers that will eat the same detritus that feeds your algae.

Third, inadequate export. A protein skimmer, refugium, or algae turf scrubber can all help here. They provide an easy way to pull things out of your water and tank without having to directly interact with the inside of the tank. Skimmer works to pull nutrients out of the water before it can fuel algae growth, refugium and algae scrubber both provide an idealized algae growth site that can outcompete in-tank algae (especially since they're not getting eaten by your CUC).

As for what I would recommend for you:

First, clean detritus off of your rocks. Blowing it off with a turkey baster or similar can work, but I actually found the Hygger aquarium brush to be really useful here. It's a waterproof powered brush with a few interchangeable heads, and I found that it honestly works really well to liberate detritus from your rocks and detach algae holdfasts from your rocks. It's definitely tricky to work around corals and I wouldn't risk it if your rocks are covered with mounted coral frags. But if you have any large expanses of rockwork that don't have corals growing on them, it can make a huge difference.

Second, add a second algae-eating fish. A one-spot foxface is a decent match for your tank size and it's one of the few critters I've seen that will occasionally attack the longer algae strands. Between that and your tang, they should keep your rocks mowed once you can get the forest cut down.

Third, if you don't already have them, add a protein skimmer and an algae turf scrubber. Both are relatively expensive so I won't say you absolutely need to do that. With that said, though, either of those would be more useful (specifically for dealing with GHA) than a UV sterilizer.

Fourth - add to your CUC. Bring in some detritus specialists (hermits, nassarius, etc). Conches can also be good here. If you don't already have any, zebra turbos are awesome algae eaters. Treat them like urchins, in that they can absolutely bulldoze frags off of your rocks, but the difference is that they'll just knock them over instead of carrying them off like a trophy.
 
Adding some or all live rock would be the first thing I would do. If you scrub the the existing rock (which I understand and don't disagree with) and rinse it in RODI its going to be very similar to starting over with dead rock and the same rock that's already proven to grow algae. Did you start with dry rock the first time? I know many succeed with dry rock start ups but when I did it my tank was a mess for over a year untill a seam failed and I broke the tank down. If I use dry rock in a display now I pack the sump full of as much live rock as I can fit and I've pretty much avoided any uglies. I don't know what causes it but I've had some rock get covered in GHA and the rocks around it remaining
 
Good luck!

Personally I would scrub the rocks and rinse with tank water. That way your beneficial bacteria won't be impacted, and you won't have to worry about any die-off polluting the new water. You'll probably want to give them a good shake in the water too. They're likely full of detritus by now.

I'd add the UV, especially since you've retained a lot of your beneficial bacteria from scrubbing the rocks in tank water. I'd run a protein skimmer too if you have one.
Thanks so much! I have been neglecting blowing off my rocks because the GHA has been maintenance priority 1. I’m sure they are loaded w detritus. I suspect the rocks and old sand (that I’ve also neglected) may be the source of GHA nutrients. I’ll get to work on the rock detritus and hook up my UV and skimmer!
 
Adding some or all live rock would be the first thing I would do. If you scrub the the existing rock (which I understand and don't disagree with) and rinse it in RODI its going to be very similar to starting over with dead rock and the same rock that's already proven to grow algae. Did you start with dry rock the first time? I know many succeed with dry rock start ups but when I did it my tank was a mess for over a year untill a seam failed and I broke the tank down. If I use dry rock in a display now I pack the sump full of as much live rock as I can fit and I've pretty much avoided any uglies. I don't know what causes it but I've had some rock get covered in GHA and the rocks around it remain algae free.
Thanks so much for your feedback! I did start with ~40% live rock (Love live rock) and had a fairly algae free tank for 4 years … I kinda like my aquascape and hate to toss it and start over w all live rock. I really like your idea of putting some new live rock in the sump
 
Thanks so much for your feedback! I did start with ~40% live rock (Love live rock) and had a fairly algae free tank for 4 years … I kinda like my aquascape and hate to toss it and start over w all live rock (even though it is so much more fun and better than dry rock). I really like your idea of putting some new live rock in the sump

Knowing that I would clean them and rinse in salt water as mentioned already to keep your bio filter going. Similar to a good ol Rip clean .

Mind if I ask what your N and P levels run? I'm just curious because any tank I've had a nuisance algae problem in has ran low N and P at or near zero.
 
GHA is complicated, but not overly so. It's almost always a combination of three factors:

First, overloading nutrients into your rocks. The waterborne nutrient number is irrelevant here - GHA is a huge nutrient sink, so it's very common to have a tank with an overgrown GHA and low or non-existent testable nutrients. Detritus settles in on your rocks and serves as in in-situ source for algae growth.

Second, inadequate consumers. Algae is everywhere. It's always going to pop up. So you need things that will eat it when it does pop up. But, once algae gets too long, your critters become disinterested in it. Too hard to eat, doesn't taste good - I'm not an algae eater, I don't know why they don't like it. I just know that they don't. So once it gets really long, your algae consumers will skip over it in favor of other sources. But on top of that, it's not just algae consumers you need. You also need scavengers that will eat the same detritus that feeds your algae.

Third, inadequate export. A protein skimmer, refugium, or algae turf scrubber can all help here. They provide an easy way to pull things out of your water and tank without having to directly interact with the inside of the tank. Skimmer works to pull nutrients out of the water before it can fuel algae growth, refugium and algae scrubber both provide an idealized algae growth site that can outcompete in-tank algae (especially since they're not getting eaten by your CUC).

As for what I would recommend for you:

First, clean detritus off of your rocks. Blowing it off with a turkey baster or similar can work, but I actually found the Hygger aquarium brush to be really useful here. It's a waterproof powered brush with a few interchangeable heads, and I found that it honestly works really well to liberate detritus from your rocks and detach algae holdfasts from your rocks. It's definitely tricky to work around corals and I wouldn't risk it if your rocks are covered with mounted coral frags. But if you have any large expanses of rockwork that don't have corals growing on them, it can make a huge difference.

Second, add a second algae-eating fish. A one-spot foxface is a decent match for your tank size and it's one of the few critters I've seen that will occasionally attack the longer algae strands. Between that and your tang, they should keep your rocks mowed once you can get the forest cut down.

Third, if you don't already have them, add a protein skimmer and an algae turf scrubber. Both are relatively expensive so I won't say you absolutely need to do that. With that said, though, either of those would be more useful (specifically for dealing with GHA) than a UV sterilizer.

Fourth - add to your CUC. Bring in some detritus specialists (hermits, nassarius, etc). Conches can also be good here. If you don't already have any, zebra turbos are awesome algae eaters. Treat them like urchins, in that they can absolutely bulldoze frags off of your rocks, but the difference is that they'll just knock them over instead of carrying them off like a trophy.
Thank you this is so so helpful!! I really appreciate all of your info. A common thread in the responses is detritus in the rocks. I will get on that right away and check out the Hygger brush. It sounds perfectly suited to my situation.

A big aha moment for me is the mention of a Foxface. I had a one-spot Foxface for years. I also had a queen conch and big tuxedo urchin and no algae problems (for 4 years). They all died around the same time which happens to be around the time the algae took off. Time to go livestock shopping!
 
Knowing that I would clean them and rinse in salt water as mentioned already to keep your bio filter going. Similar to a good ol Rip clean .

Mind if I ask what your N and P levels run? I'm just curious because any tank I've had a nuisance algae problem in has ran low N and P at or near zero.
Both run very low but since my Dino outbreak I avoid either getting to zero. P is usually .03 (I run GFO) and N was 5 last I checked. One of the reasons why I stopped skimming was bc I can’t get my N any higher and it didn’t seem to help w the GHA
 
I was curious. I know some say the algae is consuming it's and that's why they're low but I don't buy it. I have a tank that runs N 50+ and P 0.4-.09+ since starting 2 years ago and I've never had nuisance algae. I have a lot of herbivores but it was an all dry rock display / live rock sump start up and I expected to have a bad ugly phase and I had none.
200w.gif
 
I was curious. I know some say the algae is consuming it's and that's why they're low but I don't buy it. I have a tank that runs N 50+ and P 0.4-.09+ since starting 2 years ago and I've never had nuisance algae. I have a lot of herbivores but it was an all dry rock display / live rock sump start up and I expected to have a bad ugly phase and I had none.
200w.gif
Wow, your tank is gorgeous! You are for sure defying conventional wisdom that high N and P is bad. Beautiful corals! Love your tangs and your CBB is gorgeous. I miss mine..sigh. I asked the lfs to “babysit it” while I was in Italy and I came back to find out it had died (after having it 2+ yrs 😭
 
your CBB is gorgeous. I miss mine..sigh. I asked the lfs to “babysit it” while I was in Italy and I came back to find out it had died (after having it 2+ yrs 😭

I had a pair of CBB, the female had been in over 2 years and the male 14 months. The male died out of the blue. Fine then dead the next morning. A month later and the female did the same exact things. Eating well, no aggression and no tank deaths leading up to it and no deaths since. Sometimes stuff just happens and no one's to blame.
 
I wouldn't clean your live rock as described. I doubt it will solve your problem. The algae needs to be removed or killed and removed. Think of mowing your Lawn. The clippings are mulched in or lay on the Grass adding nutrients to spur new growth. As much Tank Algae as possible should be removed for 2 reasons. It will decompose in the Filter Socks and will release spores to propagate. I usually use a Cannister Filter to suck it up as I clean it and still it's tough to get rid of. Another option is to remove some Rock, use Hydrogen Peroxide to just kill it then scrub it off in a bucket and rinse it in a bucket of SW.
 
I wouldn't clean your live rock as described. I doubt it will solve your problem. The algae needs to be removed or killed and removed. Think of mowing your Lawn. The clippings are mulched in or lay on the Grass adding nutrients to spur new growth. As much Tank Algae as possible should be removed for 2 reasons. It will decompose in the Filter Socks and will release spores to propagate. I usually use a Cannister Filter to suck it up as I clean it and still it's tough to get rid of. Another option is to remove some Rock, use Hydrogen Peroxide to just kill it then scrub it off in a bucket and rinse it in a bucket of SW.
Thanks for responding. I had done this with my powerheads (h2o2 soak) and it helped slow the spread to them. I considered soaking rock too but I hate to kill all of that beneficial bacteria. Canister filter is great idea. As of now I’m doing manual removal, some brushing and filter sock. I can see how filter socks would just rerelease spores to create my never ending battle
 
If moving to a new tank is only because of the algae, I would not do it. You just need continuous export.

What do all algae (and cyano too) need to survive? Nutrients. What are nutrients? Ammonia/ammonium, nitrite, nitrate, phosphate and urea are the major ones. Which ones cause most of the algae in your tank? These same ones. Why can't you just remove these nutrients and eliminate all the algae in your tank? Because these nutrients are the result of the animals you keep.

So how do your animals "make" these nutrients? Well a large part the nutrients comes from pee (urea). Pee is very high in urea and ammonia, and these are a favorite food of algae and some bacteria. This is why your glass will always need cleaning; because the pee hits the glass before anything else, and algae on the glass consume the ammonia and urea immediately (using photosynthesis) and grow more. In the ocean and lakes, phytoplankton consume the ammonia and urea in open water, and seaweed consumed it in shallow areas, but in a tank you don't have enough space or volume for this, and, your other filters or animals often remove or kill the phytoplankton or seaweed anyway. So, the nutrients stay in your tank.

Then, the ammonia/ammonium hits your rocks, and the periphyton on the rocks consumes more ammonia and urea. Periphyton is both algae and micro-animals, and is the reason your rocks change color after a few weeks from when they were new. Then the ammonia goes inside the rock, or hits your sand, and bacteria there convert it into nitrite and nitrate. However, the nutrients are still in your tank.

Also let's not forget phosphate, which comes from solid organic food particles. When these particles are eaten by microbes and clean up crews, the organic phosphorus in them is converted into phosphate. However, the nutrients are still in your tank.

So whenever you have algae or cyano "problems", you simply have not exported enough nutrients out of your tank compared to how much you have been feeding (note: live rock can absorb phosphate for up to a year, making it seem like there was never a problem. Then after a year, there is a problem).

So just increase your nutrient exports. You could also reduce feeding, and this has the same effect, but it's certainly not fun when you want to feed your animals :)

--and--

What is Periphyton?

Periphyton is what turns your rocks different colors. You know... the white rocks you started with in saltwater, or the grey rocks (or brown wood) you started with in freshwater. After several months or years, the rocks become a variety of different colors and textures. Why? Because the periphyton that has grown on it is a mix of different living things, with different colors, and thicknesses. And the important part is: It is LIVING. And the thicker it is, the more living material there is.

That's right: The colored stuff that has coated your rocks is all living organisms. Sponges, microbes, algae, cyano, biofilms, and of course coralline in saltwater. After all, "peri" means "around the outside", and "phyto" means "plant". Have you ever slipped while walking on rocks in a stream? That's the periphyton that made it slippery. It can be a very thin coating on the rocks, sometimes paper thin, but it covers the entire surface, especially across the top which gets more light.

There is a lot of photosynthetic organisms in periphyton, and this means that they need light; but they need nutrients too (ammonia, nitrate, phosphate). And as you might guess, the organisms will prefer the illuminated portions of the rocks, and will grow to intercept food particles in the water, based on the water flow. Just think about how sponges orient their openings for water flow; the micro sponges in periphyton do it too, but on a tiny scale.

What about in caves and holes? Well periphyton here don't get much light, so they are primarily filter feeders (non-photo). So they REALLY grow and position themselves to be able to intercept food particles in the flowing water. You'll sometimes see little tree-like arms or branches sticking out to get the particles; these are usually "forams", otherwise known as foraminifera. They require a lot of food particles in the water. Think of them as coral polyps without the coral.

Reef studies have shown that at certain depths, more of the filtering of the water comes from periphyton and benthic algae, than comes from the phytoplankton which filters the deeper water. And in streams, almost all the filtering is done by periphyton because the water is so shallow. So, what you have on rocks that are "mature" or "established" is a well-developed layer of periphyton (and all the good natural things that comes from it, like nutrient absorption and food generation). They have nice colors too.

This is why mandarin fish can eat directly off the rocks of an "established" tank (tons of pods grow in and consume the periphyton), but not on the rocks of a new tank. Or why some animals can lay their eggs on established rocks, but not new ones. Or why established tanks seem to "yo-yo" less than new ones (the periphyton is a giant, self-adjusting filter). Even tangs can eat periphyton directly when it's thick enough. Yes periphyton can also develop on the sand, but since the sand is moved around so much, the periphyton does not get visibly thick like it does on rocks. So thick periphyton on established rocks is your friend. And totally natural too. That's why there are no pure white rocks in natural reefs. Keep in mind though I'm not referring to nuisance algae on rocks; I'm only referring to the layer of coloring and textures that coats the rocks, and the little arm-like structures that stick out from under rocks.

But what happens when you "scrub all the stuff off your rocks"? Well, you remove some of the periphyton, which means you remove some of your natural filter and food producer. What if you take the rocks out of the water and scrub them? Well now you not only remove more of your natural filter and food producer, but the air is going to kill even more of the microscopic sponges. And what if you bleach the rocks? Well, goodbye all filtering and food producing for another year. It's an instant reduction of the natural filtering that the periphyton was providing. So it's best to not do these things at all.

However, what if you just re-arrange the rocks? Well, some of the periphyton that was in the light, now will be in the dark; so this part will die. And some of the periphyton that was in the dark will now be in the light, so it will not be able to out-compete some photosynthetic growth and thus will be grown over and will partially die too. And even if the light is the same in the new location, the direction and amount of water flow (and food particles) will change; forams and micro sponges that were oriented to get food particles from one direction will now starve. So, since the light and food supply is cut off in the new location, the filtering that the periphyton was providing stops almost immediately, due only to your re-arranging of the rocks.

Starvation takes a little longer. The periphyton organisms won't die immediately, since they have some energy saved up; but instead they will wither away over several weeks. So on top of the instant reduction in filtering that you get by just moving the rocks, you get a somewhat stretched-out period of nutrients going back into the water. And after all this, it takes another long period of time for the periphyton to build up to the levels it was at before: 1 to 2 years. Even changing the direction of a powerhead will affect the food particle supply in the area it used to be pointed at. This is why "mature tanks" take 1 or 2 years to develop.

So a good idea is to try to keep everything the same. Pick your lighting, flow, layout, and then try to never again change anything. In other words, treat your rocks just like the rocks on a reef. It's a different way of thinking, but you should have a stronger natural filter and food producer because of it.
 
If moving to a new tank is only because of the algae, I would not do it. You just need continuous export.

What do all algae (and cyano too) need to survive? Nutrients. What are nutrients? Ammonia/ammonium, nitrite, nitrate, phosphate and urea are the major ones. Which ones cause most of the algae in your tank? These same ones. Why can't you just remove these nutrients and eliminate all the algae in your tank? Because these nutrients are the result of the animals you keep.

So how do your animals "make" these nutrients? Well a large part the nutrients comes from pee (urea). Pee is very high in urea and ammonia, and these are a favorite food of algae and some bacteria. This is why your glass will always need cleaning; because the pee hits the glass before anything else, and algae on the glass consume the ammonia and urea immediately (using photosynthesis) and grow more. In the ocean and lakes, phytoplankton consume the ammonia and urea in open water, and seaweed consumed it in shallow areas, but in a tank you don't have enough space or volume for this, and, your other filters or animals often remove or kill the phytoplankton or seaweed anyway. So, the nutrients stay in your tank.

Then, the ammonia/ammonium hits your rocks, and the periphyton on the rocks consumes more ammonia and urea. Periphyton is both algae and micro-animals, and is the reason your rocks change color after a few weeks from when they were new. Then the ammonia goes inside the rock, or hits your sand, and bacteria there convert it into nitrite and nitrate. However, the nutrients are still in your tank.

Also let's not forget phosphate, which comes from solid organic food particles. When these particles are eaten by microbes and clean up crews, the organic phosphorus in them is converted into phosphate. However, the nutrients are still in your tank.

So whenever you have algae or cyano "problems", you simply have not exported enough nutrients out of your tank compared to how much you have been feeding (note: live rock can absorb phosphate for up to a year, making it seem like there was never a problem. Then after a year, there is a problem).

So just increase your nutrient exports. You could also reduce feeding, and this has the same effect, but it's certainly not fun when you want to feed your animals :)

--and--

What is Periphyton?

Periphyton is what turns your rocks different colors. You know... the white rocks you started with in saltwater, or the grey rocks (or brown wood) you started with in freshwater. After several months or years, the rocks become a variety of different colors and textures. Why? Because the periphyton that has grown on it is a mix of different living things, with different colors, and thicknesses. And the important part is: It is LIVING. And the thicker it is, the more living material there is.

That's right: The colored stuff that has coated your rocks is all living organisms. Sponges, microbes, algae, cyano, biofilms, and of course coralline in saltwater. After all, "peri" means "around the outside", and "phyto" means "plant". Have you ever slipped while walking on rocks in a stream? That's the periphyton that made it slippery. It can be a very thin coating on the rocks, sometimes paper thin, but it covers the entire surface, especially across the top which gets more light.

There is a lot of photosynthetic organisms in periphyton, and this means that they need light; but they need nutrients too (ammonia, nitrate, phosphate). And as you might guess, the organisms will prefer the illuminated portions of the rocks, and will grow to intercept food particles in the water, based on the water flow. Just think about how sponges orient their openings for water flow; the micro sponges in periphyton do it too, but on a tiny scale.

What about in caves and holes? Well periphyton here don't get much light, so they are primarily filter feeders (non-photo). So they REALLY grow and position themselves to be able to intercept food particles in the flowing water. You'll sometimes see little tree-like arms or branches sticking out to get the particles; these are usually "forams", otherwise known as foraminifera. They require a lot of food particles in the water. Think of them as coral polyps without the coral.

Reef studies have shown that at certain depths, more of the filtering of the water comes from periphyton and benthic algae, than comes from the phytoplankton which filters the deeper water. And in streams, almost all the filtering is done by periphyton because the water is so shallow. So, what you have on rocks that are "mature" or "established" is a well-developed layer of periphyton (and all the good natural things that comes from it, like nutrient absorption and food generation). They have nice colors too.

This is why mandarin fish can eat directly off the rocks of an "established" tank (tons of pods grow in and consume the periphyton), but not on the rocks of a new tank. Or why some animals can lay their eggs on established rocks, but not new ones. Or why established tanks seem to "yo-yo" less than new ones (the periphyton is a giant, self-adjusting filter). Even tangs can eat periphyton directly when it's thick enough. Yes periphyton can also develop on the sand, but since the sand is moved around so much, the periphyton does not get visibly thick like it does on rocks. So thick periphyton on established rocks is your friend. And totally natural too. That's why there are no pure white rocks in natural reefs. Keep in mind though I'm not referring to nuisance algae on rocks; I'm only referring to the layer of coloring and textures that coats the rocks, and the little arm-like structures that stick out from under rocks.

But what happens when you "scrub all the stuff off your rocks"? Well, you remove some of the periphyton, which means you remove some of your natural filter and food producer. What if you take the rocks out of the water and scrub them? Well now you not only remove more of your natural filter and food producer, but the air is going to kill even more of the microscopic sponges. And what if you bleach the rocks? Well, goodbye all filtering and food producing for another year. It's an instant reduction of the natural filtering that the periphyton was providing. So it's best to not do these things at all.

However, what if you just re-arrange the rocks? Well, some of the periphyton that was in the light, now will be in the dark; so this part will die. And some of the periphyton that was in the dark will now be in the light, so it will not be able to out-compete some photosynthetic growth and thus will be grown over and will partially die too. And even if the light is the same in the new location, the direction and amount of water flow (and food particles) will change; forams and micro sponges that were oriented to get food particles from one direction will now starve. So, since the light and food supply is cut off in the new location, the filtering that the periphyton was providing stops almost immediately, due only to your re-arranging of the rocks.

Starvation takes a little longer. The periphyton organisms won't die immediately, since they have some energy saved up; but instead they will wither away over several weeks. So on top of the instant reduction in filtering that you get by just moving the rocks, you get a somewhat stretched-out period of nutrients going back into the water. And after all this, it takes another long period of time for the periphyton to build up to the levels it was at before: 1 to 2 years. Even changing the direction of a powerhead will affect the food particle supply in the area it used to be pointed at. This is why "mature tanks" take 1 or 2 years to develop.

So a good idea is to try to keep everything the same. Pick your lighting, flow, layout, and then try to never again change anything. In other words, treat your rocks just like the rocks on a reef. It's a different way of thinking, but you should have a stronger natural filter and food producer because of it.
Your explanation of how Rock becomes Live Rock and how surfaces a populated is spot on. The problem as I see it is we understand how the Rock is populated but are not certain why in some cases nuisance Algae begins to dominate. Nutrient Levels play a large part, however many Reefers have high nutrients but also no nuisance Algae. The OP has been battling this problem for a long time. I also have GHA and welcome any solutions Santa Monica has to offer.
 

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