The Puffer Forum

Are they junk or does anybody use them with good success?

They seem to be a thing of the past. Not too many folks use them anymore. A lot of sand and fine substrates are used as well and they render an undergravel filter useless. They are unstable for stacking rock on and really just arent nessecary. Personally, I wont use one.

I stopped using them about 25 years ago.

Reverse flow undergravel filters may still have some use when applied to the right application. But a standard undergravel setup has been superceded.
Havent used one for years and they were a right pain to sort out when they blocked up.

Yeah I haven't seen any for a long time.....I just remember when I was really young my parents tank had one. I was just wondering because I had totally forgotten about them until I saw a tank in an office today with one. Seems like they were good back when the black and white tv was good then eh. Gotta love new technology.

Undergravel filters can work very well. The reasons they aren't used are to do with aquascaping and planting, and not really anything to with their effectiveness.

On the plus side:

• Tremendous surface area for bacteria; very good water quality easily obtained.
• Low cost; filter media never needs replacing.
• Maintenance is minimal and easy.
• Work well with air stones for the low flow rates preferred by gouramis, bettas, and other still water fish.
• Also work well at high flow rates, with powerheads.
• Calcareous material can be incorporated, which is useful for buffering pH.
• Reverse-flow undergravel filters are the best for silt-free aquaria because they blow all silt into the external canister filter.

But the shortcomings are very limiting if aquascaping is important.

• Filtration depends on a uniformly deep gravel bed, 8-10 cm deep.
• Medium gravel size is best; sand can't be used.
• Filter plate needs cleaning once a year, which means the tank has to be emptied.
• Moving water through the gravel is harmful to plants, limiting options to floating plants and epiphytes.
• Anything other than minimal rockwork reduces filter effectiveness.
• Reverse-flow undergravel filters require components not widely sold in pet stores.

Bottom line, people don't use undergravel filters because the accent is usually on aquascaping and plants. But if you need lots of low-maintenance aquaria, then undergravel filters can be very economical.

Cheers, Neale

briguy44 wrote:Are they junk or does anybody use them with good success?

A standard one is junk in my opinion.. yes they can work, but they work by pulling all the waste into the substrate where it sits and rots. Not exactly ideal for good water quality, and makes a mess at clean up time... and since its such a pain to clean, you don't do it very often.

In a non-planted tank, reverse flow UG's are nice, used together with another standard hang on back or cannister filter. They keep the debris up in the water column so the mechanical filter can capture it.

I disagree. Yes, organic matter is pulled into the gravel. But with a canister filter it's pulled into the sponges or ceramic noodles. The issue is how easy is it clean the media. If you neglect either an undergravel filter or a canister filter you'll end up with clogged media.

The great advantage to an undergravel filter is that you can stir the gravel every week when you're doing water changes, and once you siphon out the organic matter, your filter is back to full operating potential. It's also important to note that most of the solid organic matter in any type of filter tends to be nitrogen-poor material: cellulose, chitin, etc. So the impact on water quality is minimal.

You can operate an undergravel filter to the same high standards as a canister filter. I did so for many years. But you do need to stir the gravel on a weekly basis, and you do need to siphon out the mulm. The fact is that many people didn't, which is why the undergravel has a reputation for being "dirty". But it remains true that even badly maintained undergravel filters still work quite well, and the reasons we don't use them have little to do with water quality as such.

Cheers, Neale

Myaj wrote:A standard one is junk in my opinion.. yes they can work, but they work by pulling all the waste into the substrate where it sits and rots. Not exactly ideal for good water quality, and makes a mess at clean up time... and since its such a pain to clean, you don't do it very often.

Doesn't the mulm wind up under the plates too? I always considered it like sweeping the dirt under the rug.

J-P raises his hand with a Q!!


I have a UGF that I have yet to put into use. It has 2 air stones under the plates. Those blow the bubbles, but in regards to the mechanics; it gets hooked up to an air pump, so how does it draw debris in?

Pufferpunk wrote:Doesn't the mulm wind up under the plates too? I always considered it like sweeping the dirt under the rug.

Yes and no. Mulm accumulates and impairs the functioning of other filters too. External canister filters have long hoses that gradually become clogged, and you need to clear those out every year. Just as much of a hassle, but unlike the cleaning of an undergravel plate, proper cleaning of canister filter hoses requires special tools. In any case, provided you stir and siphon the gravel regularly, there really shouldn't be enough mulm under the filter plate to actually cause much problem, at least if relatively small, clean fish are being kept. If you do have a messy aquarium, then a reverse-flow system works differently, and the mulm accumulates in the external canister filter.

J-P wrote: I have a UGF that I have yet to put into use. It has 2 air stones under the plates. Those blow the bubbles, but in regards to the mechanics; it gets hooked up to an air pump, so how does it draw debris in?

When air bubbles rise they draw water along with them. The further the air travels, the stronger the pull. Of course, the deeper down you put the air stone, the harder the air pump has to work, which is why a big air pump is required for deep tanks. A common mistake is to not push the air stones all the way down to the bottom of the tank. Anyway, as water rises up the filter plate tubes, that water is replaced with water drawn into the filter plate through the gravel bed. Along with the water, ammonia and debris are drawn into the gravel bed. Compared to powerheads air stones produce relatively weak currents, which makes them ideal for fish that don't like strong water currents. But it also means that you may need two or more air stones for large tanks.

Cheers, Neale

I preferred to use powerheads on the tubes, rather than the old-fashioned method of airstones.

I usually did this too. But in doing so, you lose one of the prime features of undergravel filters: good water quality, with minimal water current. A properly maintained undergravel filter is perfect for those fish that need/prefer still water conditions. The "blow" from a powerhead can be too much for gouramis, bettas, annual killifish, and various other still water fish. Much better to have two or more airstones dotted about the tank.

It's funny, but you'll often here aquarists go on about the high turnover rates required for loaches, minnows and so on. But you'll very rarely hear anyone talking about the opposite end of the water flow rate spectrum.

Cheers, Neale

Pufferpunk wrote:I preferred to use powerheads on the tubes, rather than the old-fashioned method of airstones.

I'ld say read up on the hiatt cycle, mulm is a moot point.
otherwise
dude who has a 40 year old reef tank uses an undergravel filter. his is setup in reverse, but it's the same function with backwards water flow

Can anyone explain how to reverse the flow of an undergravel filter?

I agree with you, Neale! I love air-powered filters for my bettas. I use an undergravel for my halfmoon and a sponge for my divided 2x veiltail tank. It's so easy to adjust them to exactly the right strength.