Best Way to Increase PH...

[Peer.Boerner]

Could it be that your skimmer is too small for your tank and thus not pulling enough air through the scrubber? Or have you tried cleaning your skimmer supply pump? Maybe a clog is preventing enough air being pulled into the skimmer? Sorry if these are silly suggestions but I bring them up because I run a co2 scrubber and see positive results (skimmer at or slightly above 8.3 during the day). I’m getting by with weekly water changes and no dosing just yet. Tank is fairly new with low coral load. Hope you figure it out.

 

[tzabor10]

Excellent advice @Randy Holmes-Farley
I never knew recirculating CO2 scrubbing would decrease oxygen. I run a recirculating scrubber paired with a dessicator media stage.
I do dose Kalkwasser, but lately alkalinity has been around 9.0 (Hanna)so I backed off.
pH runs around 8.6( Hanna)

 

[Rshahnyc]

Switch to NAF two part

 

[mcarroll]

I need to increase the PH of my tank. Heavy acro. Pretty new (6 months-ish). Details below.

Seems unlikely unless you have a CO2 buildup in the fish room or maybe the house itself.

[....]A lot of things that are geared towards raising PH and still it gets down to 7.9 overnight and 8.15 during the day.

I'm not sure what your goal is - those are great numbers, not low at all.

You aren't alone tho...from viewing the threads it seems like a wave of pH chasing is sweeping the hobby.

CO2 reactor seems to work sometimes and not others. I am perplexed by it. I be sure to keep fresh media in it and also a little water in the bottom of the canister. But still, its like sometimes it has a big effect and sometimes its like its not even there. The chaeto doesnt help much either. Open to suggestions on where to go with this. My thougts on options are...

Seems like you're over focused on this one issue and just looking for problems. Have you identified if you reallyu have a pH problem? At least do Randy's aeration test. If it confirms an actual issue, then try ventilating the room better. In some cases it has been as simple as leaving a door to the room open or putting a box fan in the room. Sometimes (rarely) it's a household issue and in that case a change can usually be made to the HVAC system to compensate, tho that depends on exactly what your HVAC system is like. A CO2 scrubber is not the way if you really do have a CO2 issue.

1. Install a re-circulating air setup for the skimmer. Not sure how to do this but I have read it works well.
2. Install a Kalk stirrer

That is pretty much the extent of my ideas. Any feedback would be appreciated!

I think you might mean running the air intake for the skimmer to an outside air source. *If* you actually have a CO2 issue, that can help.

Confirm your issue AND the actual source of the issue before you spend more $ and time.

(Your pH is in a great range though.....my advice, if it matters, is really to lay off this issue. Corals biologically control the pH around their skeleton growth, the water around them does not. So the perception that this is somehow important to them is mostly untrue....perhaps totally untrue.)

 

[sjfishguy]

Any coral can live at that pH, yes. But if you want acros to really grow and do the best they can, get that pH up. I started dosing kalk and it raised my pH by 0.2. I noticed a huge difference in growth of sps/acros. Even people with calcium reactors are dosing kalk too now to boost pH

 

[Randy Holmes-Farley Verified Community Expert]

Hey Randy,

So I reduced surface agitation and ran a line from outside into my skimmer and PH didnt move at all. Still 7.8-8.05ish during the day. Even with the higher PH my scrubber media doesnt seem to be saturating at all. Its still just as white as it was brand new after like 3 days. Curious if you have any thoughts on why that would be or just other ways to raise PH. Thanks for your time!

Also, I tried to DM you but the site wouldnt let me. If this would be easier and you are able to, shoot me a DM.

Are you getting good air flow into the skimmer?

 

[mcarroll]

Any coral can live at that pH, yes. But if you want acros to really grow and do the best they can, get that pH up. I started dosing kalk and it raised my pH by 0.2. I noticed a huge difference in growth of sps/acros. Even people with calcium reactors are dosing kalk too now to boost pH

That's known as the "geochemical theory" as to how coral skeleton formation works. It's an interesting theory that you won't be the last to arrive at.

But biologists have apparently held the opposing theory that the process is biologically controlled. And a consensus between the theories had never been reached until relatively recently. (More on this later.)

The "geogchamical" explanation was a good theory, even born out to an extent in lab tests. (It may even be 100% true for other critters with skeletons/shells. I don't know that, but they do point out this type of biological calcification system is not totally unique and something similar is probably happening in abalone and urchins.)

However, in 2016 it was discovered that was not the case for stony corals and that corals control the pH of skeleton formation biologically – internally, that is – and are able to modulate internal pH significantly from the water that surrounds them. (Not totally surprising given how long corals have been doing their thing.)

I posted this in 2017: "Biological control of aragonite formation in stony corals" – https://reefsuccess.com/2017/08/10/biological-control-of-aragonite-formation-in-stony-corals/

This is a great article and explains a lot.

One of their concluding statements:

[....]the biological reaction is far from thermodynamic equilibrium, and, hence, biomineralization in stony corals is not simply related to physicochemical parameters such as the equilibrium saturation state of carbonate ions or the bulk pH of seawater (33).

They also point out that corals radiated during the Eocene, a time of VERY high atmospheric CO2 levels.

Here's a depiction of the process they elucidate in the article:

Fig. 6 Working model of coral biomineralization.
Step 1, secretion of the SOM by the animal cells. Step 2, deposition of magnesium-rich ACC nanoparticles mediated by the SOM. Steps 1 and 2 might happen simultaneously. Step 3, growth of acicular aragonite crystals by attachment of amorphous precursor nanoparticles. Step 4, formation of the skeletal fibers through the “layered model” (38) of skeletal growth.

This seems to mean that higher ca and alk are the mineral factors that would really be able to increase skeletal formation rates – as we already know.

Also, this means that overall animal health is what controls skeleton formation....so that ends up including nutrition, flow and many other factors that we also currently know to be important (and inter-related).

But getting back to pH.....

Higher pH actually dictates lower dissolved ca and alk levels. ("A Simplified Guide to the Relationship Between Calcium, Alkalinity, Magnesium and pH" – https://reefkeeping.com/issues/2006-06/rhf/index.php)

At low pH (say, 7.8), much higher concentrations of calcium and alkalinity can be maintained in solution than at higher pH (say, 8.5).

Anyway...

News of that 2016 discovery didn't make it into the hobby very quickly (I doubt it's widely known even today) and old information leaves the hobby much more slowly....like never.

;)

Acro's have the same largely pH-independent process of making skeleton as other stony corals.

They do differ significantly from other corals in less mysterious ways of course, such as tissue thickness, feeding capacities and general morphology.

As such they do have some different needs and growth patterns.

One pattern commonly reported seems to be that they grow more slowly than other corals.....or that is our perception.

Another growth pattern commonly reported is that they do not seem to grow at first and then after a period put on rapid growth.

Acro's are more 3D than other corals (for self-protection), so they have more surface area than other corals. This means the growth they have is spread out over more area, leading to our perception of the first pattern – slow growth relative to other corals. (They grow VERY fast just like other corals, when they are happy.)

The second pattern (mostly about basing vs branching) is what leads some to assign growth to other factors. Frustration at the first pattern leads to folks making changes. If the changes weren't too disturbing, then pattern two happens and the rapid growth is assigned to those changes.

There's no apparent reason that a difference of 0.2 pH points is going to be significant to a coral....they are able to exert MUCH more control than that.

But other factors were surely at work, and surely you DID perceive an increase in growth....which is what really matters.

 

[Randy Holmes-Farley Verified Community Expert]

One comment on the biological control explanation: it is easier for corals to raise internal pH when the external pH is higher because it involves pumping H+ back out against the concentration gradient, and also easier for corals to take up bicarbonate and convert it into carbonate at higher bulk water pH (for the same reason).

The google AI says the energy difference to pump against an extra 0.2 pH unit difference is 1.14 kj/mole, though I did not try to validate that number.

Thus, I don’t see these theories as being mutually exclusive at all.

 

[mcarroll]

One comment on the biological control explanation: it is easier for corals to raise internal pH when the external pH is higher because it involves pumping H+ back out against the concentration gradient, and also easier for corals to take up bicarbonate and convert it into carbonate at higher bulk water pH (for the same reason).

The google AI says the energy difference to pump against an extra 0.2 pH unit difference is 1.14 kj/mole, though I did not try to validate that number.

Thus, I don’t see these theories as being mutually exclusive at all.

Well, they were attempting to examine the validity of these theories of what actually controls skeleton formation, not disprove physics. ;) ;)

But I think we must admit at a cost of "only" 1.14 kj/mole, the coral is fairly far from pH controlling skeletal growth.

Maybe like how a 1% grade slows down a V8 engine....the vehicle isn't likely slowed, it just uses a little more gas to get where it's going.

Interestingly, I found out they've studied Mediteranean corals near volcanic CO2 vents where pH was low and variable along with similar corals that were normal oceanic pH but otherwise identical water (eg temp, salinity, nutrient and food availability, etc)....I haven't seen a study like this for tropical corals so far at least.

Check these two out....they sort of go together for the discussion. The second one is the Mediterranean low-pH comparison:

"A review of the current knowledge of the flow of carbon and energy in scleractinian corals" (https://doi.org/10.1007/s00338-025-02716-8)

"High heterotrophic capacity favors Mediterranean coral success and resilience in the face of ocean acidification" (https://link.springer.com/article/10.1007/s00338-025-02663-4)

There are issues and some differences with tropical corals (they address some), but nowhere do I see them note inferior coral growth...only greater heterotrophy.

So, granted more energy consumption at lower pH, but a healthy stony coral in replete conditions isn't going to be energy limited.

To try to draw that down to our current examples, unless the coral animal is compromised somehow (e.g. poor nutrition, flow, etc.) in its ability to pump hydrogen ions, it's hard to imagine why an external 0.2 pH difference that should be well within its range would be of great significance to it.

However, if the coral animal *is compromised* in any of those ways (nutrition, flow, etc.) then we know growth would be compromised.... but the pH of the water seems practically coincidental at that point.

Looking up the range of pH on reefs, this was interesting...
"The basics of acidification: baseline variability of pH on Australian coral reefs" (https://doi.org/10.1007/s00227-010-1456-y)
...too bad the whole article isn't available, but here's a good quote...

The present study documents levels of spatial variability in pH among coral reef habitats (9 to 10), among locations separated by 100’s km of latitude and between east (Great Barrier Reef, GBR) and west (Ningaloo Reef) coasts of Australia. Differences were found in pH between inshore and offshore waters along Ningaloo Reef (means 8.45, 8.53, respectively). Replicate assessments here ranged from 8.22 to 8.64. On the GBR, the range of values over all habitats and replicates was 0.39 pH units (7.98 to 8.37). There were minor but significant differences of 0.05 pH units between 5 consecutive days for habitats on average. Highest pH was recorded in filamentous algal beds maintained by the damselfish Dischistodus perspicillatus. Lowest pH was found in water extracted from sand-dwelling goby holes.

Notably, the highest pH numbers (similar to what I've seen some folks try to target in their tanks) were not from coral habitats, but algal habitats.

Experiments
Unless there was a control tank where the CO2 levels *weren't altered* and the pH was allowed to vary naturally then it's probably pretty hard to be conclusive that raising the pH by 0.2 points – within the error rate of a pH probe? – is what actually caused a perceived change in growth.

It does seem like messing with pH could make for an interesting experiment if done right.

Back in the day we'd almost make fun of noobs for considering messing with their pH like this, but given current trends...

I wonder why nobody just hooks a bottle of pH Up (eg sodium or potassium hydroxide, or both) to a doser and a pH controller to simply anchor pH at 8.2 or 8.6 or whatever they think might be more ideal than ambient?

Seems like that would be akin to kalkwasser dosing and more straightforward than "fighting aeration" by trying to suck the CO2 out of the tank. Corals need CO2 anyway, so leave it in there.

If the theory is that "high pH" is some kind of Magic Acro Bullet™, then *just raise pH* without tweaking other relevant factors and see what happens. Also have another identical tank with identical corals but where pH is not raised and see what happens there too. Hopefully that comparison of results would tell us something. But I'll bet that experiment would be trickier to do well than it sounds on the surface.

 

[sjfishguy]

Any coral can live at that pH, yes. But if you want acros to really grow and do the best they can, get that pH up. I started dosing kalk and it raised my pH by 0.2. I noticed a huge difference in growth of sps/acros. Even people with calcium reactors are dosing kalk too now to boost pH

That's known as the "geochemical theory" as to how coral skeleton formation works. It's an interesting theory that you won't be the last to arrive at.

But biologists have apparently held the opposing theory that the process is biologically controlled. And a consensus between the theories had never been reached until relatively recently. (More on this later.)

The "geogchamical" explanation was a good theory, even born out to an extent in lab tests. (It may even be 100% true for other critters with skeletons/shells. I don't know that, but they do point out this type of biological calcification system is not totally unique and something similar is probably happening in abalone and urchins.)

However, in 2016 it was discovered that was not the case for stony corals and that corals control the pH of skeleton formation biologically – internally, that is – and are able to modulate internal pH significantly from the water that surrounds them. (Not totally surprising given how long corals have been doing their thing.)

I posted this in 2017: "Biological control of aragonite formation in stony corals" – https://reefsuccess.com/2017/08/10/biological-control-of-aragonite-formation-in-stony-corals/

This is a great article and explains a lot.

One of their concluding statements:

[....]the biological reaction is far from thermodynamic equilibrium, and, hence, biomineralization in stony corals is not simply related to physicochemical parameters such as the equilibrium saturation state of carbonate ions or the bulk pH of seawater (33).

They also point out that corals radiated during the Eocene, a time of VERY high atmospheric CO2 levels.

Here's a depiction of the process they elucidate in the article:

Fig. 6 Working model of coral biomineralization.
Step 1, secretion of the SOM by the animal cells. Step 2, deposition of magnesium-rich ACC nanoparticles mediated by the SOM. Steps 1 and 2 might happen simultaneously. Step 3, growth of acicular aragonite crystals by attachment of amorphous precursor nanoparticles. Step 4, formation of the skeletal fibers through the “layered model” (38) of skeletal growth.

This seems to mean that higher ca and alk are the mineral factors that would really be able to increase skeletal formation rates – as we already know.

Also, this means that overall animal health is what controls skeleton formation....so that ends up including nutrition, flow and many other factors that we also currently know to be important (and inter-related).

But getting back to pH.....

Higher pH actually dictates lower dissolved ca and alk levels. ("A Simplified Guide to the Relationship Between Calcium, Alkalinity, Magnesium and pH" – https://reefkeeping.com/issues/2006-06/rhf/index.php)

At low pH (say, 7.8), much higher concentrations of calcium and alkalinity can be maintained in solution than at higher pH (say, 8.5).

Anyway...

News of that 2016 discovery didn't make it into the hobby very quickly (I doubt it's widely known even today) and old information leaves the hobby much more slowly....like never.

;)

Acro's have the same largely pH-independent process of making skeleton as other stony corals.

They do differ significantly from other corals in less mysterious ways of course, such as tissue thickness, feeding capacities and general morphology.

As such they do have some different needs and growth patterns.

One pattern commonly reported seems to be that they grow more slowly than other corals.....or that is our perception.

Another growth pattern commonly reported is that they do not seem to grow at first and then after a period put on rapid growth.

Acro's are more 3D than other corals (for self-protection), so they have more surface area than other corals. This means the growth they have is spread out over more area, leading to our perception of the first pattern – slow growth relative to other corals. (They grow VERY fast just like other corals, when they are happy.)

The second pattern (mostly about basing vs branching) is what leads some to assign growth to other factors. Frustration at the first pattern leads to folks making changes. If the changes weren't too disturbing, then pattern two happens and the rapid growth is assigned to those changes.

There's no apparent reason that a difference of 0.2 pH points is going to be significant to a coral....they are able to exert MUCH more control than that.

But other factors were surely at work, and surely you DID perceive an increase in growth....which is what really matters.

Nice theory. My eyes and experience show that higher pH increases growth rate, no question