Paul B
Premium Member
What happened to under gravel filters?
Tropical fish keeping in the US started just after WW2 as people were coming back into civilian life and started looking for a hobby.
Freshwater fish were cheap and available as "toy" fish and sold in toy stores.
The filtration on those early tanks were normally an air powered hang on back filter or an in tank, air powered box filter filled with fiberglass floss (nasty stuff). The bottom of the tank used gravel, sometimes colored gravel and under that was an under gravel filter.
The purpose of the UG filter was to remove particles from the water and augment the fiberglass floss in the box filters. They worked well and we were happy with our fresh water tanks and they gradually became more technical and the fish varieties grew.
Then in 1971 saltwater fish were imported into the US and many people, myself included just couldn't resist setting up a salt tank.
We already had fresh water tanks, filters, air pumps and the old stand by, an undegravel filter.
If it worked in fresh water it should also work in saltwater, right?
So we set up our salt water tank by first installing an under gravel filter, then adding crushed coral or dolomite. The UG filter was operated with an airstone that pulled water up through the tubes there by forcing water to go through the gravel.
The device operated as a mechanical filter and trapped all the nasty things that we didn't want in our tank. We never realized that after you trap all that stuff, it stays there and rots. We didn't realize that it is the bacteria that is supposed to eliminate the wastes and not the gravel.
Our tanks ran well for about a year, then something happened that we could not understand. They were crashing, the fish were full of disease and in some cases the water stunk. When we stirred the gravel, it really stunk which forced us to remove everything from the tank, clean it, change the water and buy new fish.
Then in the late 70s and 80s other systems started to become common such as wet drys, Jaubert, bare bottom etc. and UG filters were removed and thrown out with the garbage never to be seen again.
In my opinion, that was a mistake and I still use mine. The problem was not the under gravel filter, but the way we used it. The device was designed to work a specific way in freshwater and needed to be modified to run in a salt tank.
The modification is simple, it just involves running it in reverse and slowing it down a bit.
We also need to filter or at least strain the water entering it. Most UG filters use two, three or four uplift tubes and it is complicated to pump water down all those tubes so I remidied that problem by piping all the tubes together in a single manifold where water is pumped into after having gone through a sponge filter. This sponge removes any larger pieces of detritus or food that would get pumped under the gravel. Of course this will not remove all the particles but will greatly help with the maintenance of the device.
This system actually needs some detritus to run correctly and will not work until some time has passed. Bacteria needs time to colonize the surfaces of the gravel and the detritus that will eventually form between the grains of gravel will slow down the flow of water creating places where anerobic bacteria will grow.
It will never achieve the nitrate reducing capabilities of a DSB but the fact that it can be maintained insures that it can last forever. The only maintenance needed is to occasionally rinse the sponge filter and once or twice a year stir up the gravel where you can, with a canister filter.
Noting will run forever without maintenance and I feel that this hour or two of maintenance a year is not that overwhelming.
The system is also very forgiving and in the 42 years that mine has been operating my power has gone out quite a few times, sometimes for days and there has never been a problem. I once had a very large carpet anemone die and decompose sending pieces of rotting anemone all over the tank, but nothing happened.
I used to have an urchin collection business and one time I had to many urchins so I put 24 of them in my reef where they all spawned at the same time. The water looked like Half and Half, the five gallon bucket I have under my skimmer that collects the effluent overflowed and I guess about 8 gallons of water was removed from the tank,
and still, after I cleared the water with a diatom filter, nothing happened.
The tank houses SPS and LPS corals along with three pairs of spawning fish one of which is a 19 year old fireclown.
The tank has never crashed and has never been emptied except once in 1979 when I moved to a new house and transfered everything into the tank in my new home.
The key is to run the device slowly. The slower it is run, the less detritus will be trapped and the longer it will run without maintenance. My tank is 100 gallons and I pump about 500 GPH into the manifold where it equally seperates the water to flow down each tube and under the gravel.
I am certainly not trying to convince anyone to use an UG filter. My purpose is just to educate about a device that used to be the backbone of the hobby.
I use this old green HOB filter container as my manifold where the 3 tubes come out of the bottom and travel to the UG filter plates under the gravel. Water is pumped into the manifold through that tube on the left.
Tropical fish keeping in the US started just after WW2 as people were coming back into civilian life and started looking for a hobby.
Freshwater fish were cheap and available as "toy" fish and sold in toy stores.
The filtration on those early tanks were normally an air powered hang on back filter or an in tank, air powered box filter filled with fiberglass floss (nasty stuff). The bottom of the tank used gravel, sometimes colored gravel and under that was an under gravel filter.
The purpose of the UG filter was to remove particles from the water and augment the fiberglass floss in the box filters. They worked well and we were happy with our fresh water tanks and they gradually became more technical and the fish varieties grew.
Then in 1971 saltwater fish were imported into the US and many people, myself included just couldn't resist setting up a salt tank.
We already had fresh water tanks, filters, air pumps and the old stand by, an undegravel filter.
If it worked in fresh water it should also work in saltwater, right?
So we set up our salt water tank by first installing an under gravel filter, then adding crushed coral or dolomite. The UG filter was operated with an airstone that pulled water up through the tubes there by forcing water to go through the gravel.
The device operated as a mechanical filter and trapped all the nasty things that we didn't want in our tank. We never realized that after you trap all that stuff, it stays there and rots. We didn't realize that it is the bacteria that is supposed to eliminate the wastes and not the gravel.
Our tanks ran well for about a year, then something happened that we could not understand. They were crashing, the fish were full of disease and in some cases the water stunk. When we stirred the gravel, it really stunk which forced us to remove everything from the tank, clean it, change the water and buy new fish.
Then in the late 70s and 80s other systems started to become common such as wet drys, Jaubert, bare bottom etc. and UG filters were removed and thrown out with the garbage never to be seen again.
In my opinion, that was a mistake and I still use mine. The problem was not the under gravel filter, but the way we used it. The device was designed to work a specific way in freshwater and needed to be modified to run in a salt tank.
The modification is simple, it just involves running it in reverse and slowing it down a bit.
We also need to filter or at least strain the water entering it. Most UG filters use two, three or four uplift tubes and it is complicated to pump water down all those tubes so I remidied that problem by piping all the tubes together in a single manifold where water is pumped into after having gone through a sponge filter. This sponge removes any larger pieces of detritus or food that would get pumped under the gravel. Of course this will not remove all the particles but will greatly help with the maintenance of the device.
This system actually needs some detritus to run correctly and will not work until some time has passed. Bacteria needs time to colonize the surfaces of the gravel and the detritus that will eventually form between the grains of gravel will slow down the flow of water creating places where anerobic bacteria will grow.
It will never achieve the nitrate reducing capabilities of a DSB but the fact that it can be maintained insures that it can last forever. The only maintenance needed is to occasionally rinse the sponge filter and once or twice a year stir up the gravel where you can, with a canister filter.
Noting will run forever without maintenance and I feel that this hour or two of maintenance a year is not that overwhelming.
The system is also very forgiving and in the 42 years that mine has been operating my power has gone out quite a few times, sometimes for days and there has never been a problem. I once had a very large carpet anemone die and decompose sending pieces of rotting anemone all over the tank, but nothing happened.
I used to have an urchin collection business and one time I had to many urchins so I put 24 of them in my reef where they all spawned at the same time. The water looked like Half and Half, the five gallon bucket I have under my skimmer that collects the effluent overflowed and I guess about 8 gallons of water was removed from the tank,
and still, after I cleared the water with a diatom filter, nothing happened.
The tank houses SPS and LPS corals along with three pairs of spawning fish one of which is a 19 year old fireclown.
The tank has never crashed and has never been emptied except once in 1979 when I moved to a new house and transfered everything into the tank in my new home.
The key is to run the device slowly. The slower it is run, the less detritus will be trapped and the longer it will run without maintenance. My tank is 100 gallons and I pump about 500 GPH into the manifold where it equally seperates the water to flow down each tube and under the gravel.
I am certainly not trying to convince anyone to use an UG filter. My purpose is just to educate about a device that used to be the backbone of the hobby.
I use this old green HOB filter container as my manifold where the 3 tubes come out of the bottom and travel to the UG filter plates under the gravel. Water is pumped into the manifold through that tube on the left.
