Can someone please tell me what are the advantages, and best uses for under grave filters, and mechanical sponge type filters?

I keep hearing how bad undergravel filters are, especually when its your only filter system....

When I had gold fish and undergravel filter, I noticed that it would collect all the gunk either in the gravel (good i guess), trap and block teh grill 0part (bad) or live underneath the filter where it stays (also bad but prob cos i used air reather then power head to move water....). Dont know how long it is meant to take for poop to break up but I got rid of it pretty quickly cos of the gunk I coudlnt clean out without taking apart the tank....

Lots of people talk online out adding it in reverse for external canister filters (attacked to the out) and have always wanted to try this as it may stop the gunk staying in teh gravel and make cleaning easier.....

If using one, I would suggest one with a power ehad and good grill that wont get blocked easily.

My 2 cents, quite keen to see what others think on it too.... currently I just use external canaisters and they have done me well :-)

I love undergravels for small tanks (up to 2ft) but not for goldfish. Goldfish are messy and continually digging in the substrate which upsets the plates. They are suitable for small tanks for small fish that don't nosey through the substrate.

I have never had to strip a tank to clear out an undergravel. They are supposed to amass gunk under the plates - that is where the good bacteria live and work. It is good gunk and not meant to be cleared out.

You need at least 5cm of substrate on top if you want to grow plants well though.

They are good for fish that prefer slower moving water as they don't produce the flow you get from canisters.

I prefer them to internals as they are out of sight, except for the uplift, and don't take up space like the internals.

Sponge filters are great in fry tanks as the fry don't get sucked up the filter.

I was told once that with the undergravel filter - if you had a power cut or air pump stopped working then the toxins rised - is this true or just a myth?

Caryl i'm intrigued ... 2 days for what (may I ask)

That will be so with any filter. In a power cut the bacteria start dying very quickly without the water going through.

I am sure you will find out in 2 days Mel

It isn't anything particularly interesting to anyone but me :roll:

See, with undergravel filters, I was never really sure of this.... do you clean it with gravel vac etc to get the crud out or do you let the filter do its own thing and just do normal water changes.... in which case the stuff accumulates until its broken down by the bacteria, tehrefore water chnage is just to decrease nitrates.

I used to think the 2nd one but when was told to go with gravel vac which i thought would create an imbalance of bacteria etc and cause issues....

The REAL filtration is bacterial action on chemicals in the water, NOT breakdown of solid wastes.

With other types of filter, you don't want the solid wastes clogging up the filter media, so you try to stop as much of that getting to the filter media as possible.

I always felt this was true for undergravel filters. You should gravel vac out the solid wastes otherwise with enough time it will clog and render it useless.

MatthewY, air-driven uplifts move more water than you would expect. I saw a fascinating article once about it where someone calculated it against commonly-used small powerheads. The reason they seem not to move much is because the water is not coming out of a small hole with directional force.

I vacuumed mine with no problems. I just wasn't super thorough about it.

The REAL filtration is bacterial action on chemicals in the water, NOT breakdown of solid wastes.

With other types of filter, you don't want the solid wastes clogging up the filter media, so you try to stop as much of that getting to the filter media as possible.

I always felt this was true for undergravel filters. You should gravel vac out the solid wastes otherwise with enough time it will clog and render it useless.

MatthewY, air-driven uplifts move more water than you would expect. I saw a fascinating article once about it where someone calculated it against commonly-used small powerheads. The reason they seem not to move much is because the water is not coming out of a small hole with directional force.

I guess it depends on your definition of small powerheads. I don't see an air driven one moving 1000+lph.

I guess it depends on your definition of small powerheads. I don't see an air driven one moving 1000+lph.

Ah, but then a 1000lph isn't a small common powerhead, most normal people call small 100 - 300 lph!!

also most 1000lt+ powerheads wouldn't fit on the average undergravel filter!

Ah, but then a 1000lph isn't a small common powerhead, most normal people call small 100 - 300 lph!!

That's practically microscopic. A 1300lph power head with a smaller intake than most undergravel filters costs about $30 the last time I bought a couple.

That's practically microscopic. A 1300lph power head with a smaller intake than most undergravel filters costs about $30 the last time I bought a couple.

sounds good would you mind pming me where to get them from? 8)

Sorry, they're 1100 liters per hour, Via Aqua VA 1300s. I got two of them from my LPS a couple years ago, had one force feeding my 404 with a dead motor for a couple years.

so do you connect the power head to the under gravel filter insteed of an air blower?

I've heard of people using under gravel filters and reversing the flow. So it pumps water in, rather than sucking water out.

Any thoughts on the two methods? I'd think that the reverse method would work better for some reason.

sometimes people use the reverse method as well as other filtration as it helps keep the gravel clean. both ways are great filters and are often underestimated

Regarding pumping in. This would stop fish waste from settling in the gravel so much - in which case : where is it supposed to go? I understand pumping it out for greater flow rate, specially with thinner gravel which will get hotspots of flow. But pumping in would only be useful in my mind to add addition filtration following a cannister or sumps' prefiltering of solid wastes... in which case it adds a level of water polishing and just keeps the gravel aerobic.

Given a chance bacteria will eat solids. I'm sure the math is possible to calculate surface area, flow rates and media quantity to give a stable aquarium requiring little or no vacuuming (using an undergravel).

Personally I've found undergravels too tricky for reliable filtration on their own. If I get the chance and can have the depth I use one just to keep everything aerobic and healthy. Whatever fish waste gets stuck under rocks etc, as it invariably does, will get eaten by something eventually - where it is or when it eventually goes back into the water system and gets eaten by something else...

Yeah it just goes on top, sending the water out. so you get more movement and airation and more pull...