Someone asked me how a Reverse Undergravel Filter works and what is the advantage.

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Paul B

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Someone asked me how a reverse Undergravel filter works and what is the advantage of it.
In the beginning, when we all kept bait, I mean fresh water fish we all ran undergravel filters. That was the only way to go and in fresh water they work perfectly.

When salt water started for home tanks in 1971 in the US (a little before that in Europe) some of us switched our tanks to salt but we kept our UG filters. Most of us did change the gravel to something different than the purple broken glass we had in fresh water and we removed the sunken chests and deep sea divers fighting sharks but there was no salt water gravel available.

After unsuccessfully using blue driveway gravel I discovered dolomite. You can still get it at a mausoleum or museum, maybe an archaeological dig in Egypt, I don't know but I assume crushed coral would also work.

I first ran my salt tank using a normal UG filter and in less than a year it crashed and I had to rescue my fish. There was no coral, live or dead rock then but we did have bricks, cinder blocks and roller skates. Much of my "rock" was asphalt that was dumped in the sea before I was born. I still have some of it and if you look close you can probably see remnants of the yellow line that was painted on it when it was a street. :oops:

I am not sure what the problem was by using a UG filter the normal way. We didn't have powerheads so they were all run with bubbles and they didn't run to fast but the salt creep on the lights caused us to have to turn on the lights with a stick because GFCIs were also not invented. As a matter of fact, to do anything on the tank we had to unplug everything and the only thing we could keep with success was electric eels. :rolleyes:

Anyway, the UG filters, after a few months became totally clogged rendering them useless similar to some politicians.

I decided to reverse the thing and instead of the water going down through the gravel, now it came up through the gravel. Something happened. It was a good thing. The tank didn't crash. It kept going and fifty years later it is still running.

Not crashing is a good thing but not the only benefit. I learned from Robert Straughn "The Father of Salt Water Fish Keeping" that the bottom of the tank is the perfect filter and the largest thing in the tank. Mr. Straughn used UG filters constantly but at that time, in the 50s he didn't quite understand the function of bacteria like we do today and he used the filter as a particle filter.

That works but you have to clean it constantly and as a whole, humans are lazy.
I discovered that if you pump water through the gravel at a slow speed and maybe strain it of particles first, the thing would not only last forever, 50 years anyway, but the tank would thrive and it would be easier to keep smaller fish.

A sand bottom has very little oxygen going through it as it is stagnant. But gravel, even if it is just sitting there has water flowing all through it. But if we give it a little help and push a little water through it, multitudes of creatures colonize it causing it to be a huge eco system.

Tiny tube worms, brittle stars, pods and bacteria completely fill every void. Those tube worms filter the water and the brittle stars remove particles. Very little detritus is left and a little detritus is good because it even provides more living space for those creatures which hate clean, sterile places to live sort of like Ozzie Osborn.

Those tiny creatures can breed in multitudes feeding smaller fish like pipefish, mandarins, dragonettes and anything that eats pods. I have many of those fish, they are all spawning and I never have to feed them.

This silly thing is the manifold I used for many years. I built a new one now but it is the same principal.
It is of course an old HOB filter. The three tubes coming out the bottom go to each of the 3 UG filter tubes.

The one on the left doesn't do anything and was a mistake, it is blocked.

Water is pumped into the thing from that hose on the left. I don't have a sump or I would have to divert some water from that to here.

I run about 250 GPH down each tube so about 500 GPH is pumped into the manifold where the water is evenly separated. Faster flow is no good, it has to be slow.

Once or twice a year I stir up the gravel where I can reach with a canister filter or diatom to remove excess detritus. If it was left forever it would probably clog eventually and besides, I like doing it.

Of course if your present system lasted longer than fifty years, do that. ;Joyful

 
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DaddyFish

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There are definitely two "camps" when it comes to filtration; rapid flow cleaning away everything possible, and very slow flow letting nature/bacteria do most of the work.

I think there's a lot to learn from your setup but I'm a numbers guy! Any chance you can quantify some things about your setup like...

* 500 gph per what dimensions of UG filter?
* Have you run this setup on tanks of significantly different dimensions (especially height) and is there a varied requirement for filter area based on height/depth of the tank?
* What fish stocking density have you achieved or maintained with this setup?
 

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I run an RUGF on a 90 gallon. 2 plates with a 650gph pump supplying both. Avg of 275 going to each. I have clowns, gobies, blennys mandarins and a tang. Also nems, leathers, palys. Tank has been running for 2 years. Same as Paul I don't QT anything and feed diverse real food.

16152308363335077506616569500440.jpg
 
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Paul B

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The tank is a 125 gallon, so 6' long. The UG filter has 3 plates that cover the entire bottom of the tank.

The tank has been running constantly since 1971 but the glass was much smaller at first. It was in a 40 gallon tank for a few years, then in a 100 gallon tank for 40 years and that 100 gallon had almost the same footprint of the 125 gallon tank I have now.

I have about 25 fish of varying sizes, mostly small like wrasses. The largest fish are a copperband, long nose butterfly and hippo tang. There are also a couple of almost 30 year old fireclowns.



Here are some of the fish with the pumps off. I have very strong flow with the pumps on.

 
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Jekyl

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The tank is a 125 gallon, so 6' long. The UG filter has 3 plates that cover the entire bottom of the tank.

The tank has been running constantly since 1971 but the glass was much smaller at first. It was in a 40 gallon tank for a few years, then in a 100 gallon tank for 40 years and that 100 gallon had almost the same footprint of the 125 gallon tank I have now.

I have about 25 fish of varying sizes, mostly small like wrasses. The largest fish are a copperband, long nose butterfly and hippo tang. There are also a couple of almost 30 year old fireclowns.



Here are some of the fish with the pumps off. I have very strong flow with the pumps on.

What's the bottle count up to in there now?
 

Jekyl

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That's very cool! I wish it was practical to capture a sample from those uprising bubbles for gas analysis, but that's beyond my resources.
I never get any gas rising from underneath that I notice. Every time I'm by the tank I grab the pump cord to make sure it's still running. I know it's doing its job though. My mandarin is the fattest fish in my tank and I haven't added pods in over a year now
 
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Paul B

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I think there are about 9 of them but most of them are so covered I can't find them. :cool:

I never bought a pod in my life
 

DaddyFish

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I never get any gas rising from underneath that I notice. Every time I'm by the tank I grab the pump cord to make sure it's still running. I know it's doing its job though. My mandarin is the fattest fish in my tank and I haven't added pods in over a year now
There's a lot of gas bubbles rising in PaulB's video. They're everywhere!
 
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Jekyl

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The thing that attracted me to this type of tank is the counter to the retail push of products. It was the oldest system I had found and for the most part went a different direction than most of the products and technology being thrown around for high prices.
 
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Paul B

Paul B

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Those tiny bubbles you see when the pumps are off come from the algae. Algae makes oxygen. With the pumps running like here, there is all sorts of stuff floating around, just as I like it.
I must have just fed them here.

 
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Paul B

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The thing that attracted me to this type of tank is the counter to the retail push of products. It was the oldest system I had found and for the most part went a different direction than most of the products and technology being thrown around for high prices.
Remember the tank was set up way before any companies sold anything for salt water, And I don't use any products. I built just about everything.
 

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Here's a question for you Paully- B....do you dose anything to that tank to maintain calc & alk ? or do you just allow the aragonite material to supply it as the PH dips at night ?
 
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Jekyl

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Mine ranges between an inch to 3. I've never had to add any more than I started with. Few times a year I'll vacuum it or move it around to clean up after my pistol shrimps mess. Haven't had any real issues with parameters yet.
 
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Here's a question for you Paully- B....do you dose anything to that tank to maintain calc & alk ? or do you just allow the aragonite material to supply it as the PH dips at night ?
Remember most of that gravel has been in there for 50 years so I do have to dose calc and alk. When the hobby started we didn't dose or test because there were no live corals so I don't know if it dissolved anything then. Not much I would guess.
Cool beans! How deep is the gravelbed? Do you ever fill up the gravel (ie, is it consumed because of lower pH in bottom layers when (if?) it ever goes anoxic?)? Thanks for sharing!
My gravel is only about 2-3". It has never gone anoxic and I didn't have to add more except when I put it in a larger glass.
 

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I was talked into putting a Reverse Flow under gravel in my 90 gallon. It was actually a little smaller than the sand bed, due to the corner overflow. All my Copepods and Amphipods disappeared. Added another culture, they didn’t stay either. The Bristle Worms loved it.
 
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