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

[OrionN]

When I had FW tank I used underavel filter. I keep Oscar and feed the earthworms sometime. The ones that escaped their fated live in the under gravel filbert and reproduced in the gravel. This system was stable and never crashed. The earth worm actually keep the filter clean.

When I started to keep marine tank, I start out with under gravel filers with dolomites. It did not crashed on me but I used canister filter. Eventually I decided it would run better with reverse filter and plumbed it so.

I got hold of a few bristle worms and added them to the substrate and got a population going. It was perfect. Never crash and the filter never clots up. That is the advantage of reverse flow. Prior to send it through the substrate, if it get particle filtration the filter would last forever, especially if you get some sand bed creatures to eat what little organic fall on to it.

 

[Subsea]

My point isn't that the RUGF isn't useful/valuable, just that there's no great premium for reverse flow as opposed to normal flow.

I can expound on this point. In all plenum sandbeds, channeling of flow up thru substrate can lead to dead spots in substrate which produce anarobic biochemistry. From my experiences, I have no need for more denitrification in 25 year mature sandbed, as I already dose ammonia for nitrogen makeup. If channeling of flow occurs as an up flow filter, I can visually see this sand volcano on top of substrate.

 

[Sophie"s mom]

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.

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.

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

Man do I wish I had come across this before I set my tank up in September! I still have old under gravel plates, but reading about how out dated they are, I opted not to use them, and just go with straight live sand. I know that eventually I will need to remove and deeply clean this sand. At that point, I believe I will switch to your system, as I still have the plates.

 

[GARRIGA]

Reminds me of the "tufa rocks" that were available in the 00's. I havent seen them for sale anywhere and they were a great rock, lighter and more porous, and cheaper, than the dry rock available now, kept the ph buffered and didnt leach anything.

I used Tufa rocks. Haven’t seen those for sale since the 90s as well.

 

[GARRIGA]

Me thinks attaching the undergravel lifts to a canister where one occasionally stirs the gravel to unclog channeling and move mulm to the canister where it can be disposed of efficiently the best of both worlds. Largest surface area vs current practice. Flow can be reduced to encourage denitrification although considering depth of gravel that might be futile. Although feeding it might help. Only maintenance being the occasional gravel stirring and canister cleaning. Add UV-C and ozone or h2o2 post canister and it will help further cleanse the return water. Latter can be 24/7 or ran as needed. Sure would reduce the need for many apparatus for which I often think the hobby keeps because either feel there’s a marketed need or some are just gear junkies.

KISS.