someone explain undergravel filters to me

[FastFly67]

i think i'm dumb. which direction does it pull the water from? if it pulled the water down, doesn't all your icky stuff get stuck in your gravel. if it pushes up from the gravel, isn't all your junk floating. help me understand please

 

[CaptainAhab]

You can run it either way. To run it reverse, water flowing up thru your gravel you have to use a powerhead(s). If you use airstones then it will flow down thru your gravel. Don't let people discourage you from using them for FW tanks. They are easy to keep clean by building a small contraption that will hook to a shopvac.

They are a GREAT biological filter.. hands down

 

[jsoong]

The traditional UGF pulls the water down into the gravel. The icky stuff is supposed to get trapped in the gravel bed & break down. The concept is great, but lots of people have problems with cleaning under the plates so UGF had gone out of favor. <I've not tried CaptainAhab's idea of using a shopvac to clean under the UGF .... sounds like a good work around.>

The other way of using the UGF is reverse flow. You use a power head to push water under the plates. This forces all the junk out of your gravel, and you will need a second filter (HOB or canister) to collect it all. Advantage of this is keeping the gravel clean & well aerated (no risk of anoxic pockets & no need for gravel vac). But you will be running 2 filters.

 

[gheitman]

A few things that might not have been made clear is that with the under gravel filter (aka UGF) the aquarium gravel serves as the medium for the bacteria necessary to break down the waste. You need to make sure that the UGF plates don't get exposed by fish digging in the gravel otherwise the water flow won't go through the gravel at all. Also, if you are planning on keeping live plants UGF is not usually the best way to go (RUGF or reverse under gravel filter is the exception although still not the best IMO).

 

[kimo]

My UGF system:

150 gallon tank housing adult fancy guppies (app 300-500 at any one time)
Other inhabitants are a small colony of Red Cherry Shrimp, 3 Ghost Shrimp and 12 Neon Tetras (3 are more than 8 yrs old). Approx 200+ low/medium light plants of all types. Gravel is 3/16" standard natural pea gravel mixed with shell grit. Decorative stones are mostly Lava collected in the desrt SW. Largest is 14x8x6" Approx 200 lbs all covered with Java moss and/or guppy grass. Tank has been set up for 10 yrs + this location (38 yrs total). The UGF covers the full bottom w/3 - 4" thickness of gravel on top. No air pumps or jet pumps used. No other filters used except to polish water (cannister/Diatom) after a water change (50% 2-3x a yr) for about 3 hours.

UGF installed and running normally for the first 8 months after setup to establish bacteria colony (cycle with fish/plants). Plants were introduced a few at a time since setup. Fertilizer used is PMDD+CSMB (225 mL/week) but will change over to individual ferts once the PMDD is used. After breakin and cycle UGF flow was turned down a little each month over 6 months until completely off. No vacuuming of the gravel ever. Fish are fed 3 - 8X daily 6 days a week but only an amount for them to clean up within 1 or 2 minutes. 95% of food never reaches bottom. If I have a dirty spot on the bed I will feed fish sinking shrimp pellets in that area and it will be spotless within 3 days. No algae growth anywhere except green spot algae near lights. Front glass scraped monthly. Tank simulates a dry season stream pocket w/plants, cut off from main flow.

When I change water (50%) to get rid of TDS, I use a 3/4" plastic hose stuck down one of the lift tubes. Always draining from lowest point in tank (beneath UGF plates). Roots from the plants have really not bothered imbedding in the filter plate yet... one or two Crinum are the only ones entangled and that took 4 yrs. The bio-load is light compared to a cichlid tank setup but I still think this method would work with them too IF tank was never overloaded with fish. Infusoria and microscopic life are a good thing. No mulm ever collects. Nitrates always run below 40 - 50 ppm. I can leave for 3 -6 weeks without fear of no food/starvation. There has never been disease of any type. New fish and plants are always Qt'ed at least 3 weeks.

The trouble most people have with UGF's is overfeeding which leads to plugging the gravel bed. Then they vacuum and leave nothing behind. A spotlessly clean tank is a diseased tank just waiting to happen (does not apply to SW). The area under the filter plate is as clean now as it was 10 years ago. Never a problem with aenorobic bacteria.

Try this method... you will have to experiment at first to get the right balance of fish/plants/filter bed. Once you get it right you can put all the LFS'es out of business because you won't need all the extra supplies they pile on you.

 

[goldmanjace]

Do ugf work with sand also?

 

[gheitman]

No, because the sand will fall through the slits in the filter plates and block underneath.

 

[goldmanjace]

That is what I thought. What would the best filter system be if sand was used? I am talking about a 55 G tank. I have 2 30/60 waterfall filters but I am used to filters outside of the tank like the eheim and jbl filters that go under the aquarium stand. The tank is not up and running yet.

 

[gheitman]

I prefer canister filters for my tanks that are planted and about 30 gallons in size and sponge filters for most of my tanks that are 20 gallons or smaller. I do have power filters on one 29 gallon that isn't heavily planted and on one ten gallon that I needed higher water flow. I would think that either a canister filter or a power filter would work (or perhaps one of each to give redundancy) depending on the population of your tank. One thing you need to look out for is not putting the intake tube for your filter(s) too near the bottom of the tank so that sand doesn't accidentally get sucked in.

 

[goldmanjace]

I prefer canister filters for my tanks that are planted and about 30 gallons in size and sponge filters for most of my tanks that are 20 gallons or smaller. I do have power filters on one 29 gallon that isn't heavily planted and on one ten gallon that I needed higher water flow. I would think that either a canister filter or a power filter would work (or perhaps one of each to give redundancy) depending on the population of your tank. One thing you need to look out for is not putting the intake tube for your filter(s) too near the bottom of the tank so that sand doesn't accidentally get sucked in.

What exactly is a power filter? Is that a powerhead??

 

[gheitman]

A power filter is also known as a hang on back (aka HOB) filter and literally hangs on the back of the tank. It is something along the lines of the Hagen AquaClear 50 or the Marineland Emperor 400. These are probably the most preferred filters for general usage because they combine biological, chemical and mechanical filtration methods in one easy to maintain unit. A power head is a water pump that can be submerged in a tank to help water circulation or provide suction for air filters and under gravel filters (aka UGF). An example of this would be the Hydor Koralia. The two aren't mutually exclusive. Power heads can be used in tanks that already have filtration to make sure there aren't any 'dead spots' where water doesn't circulate properly.

 

[sumpnfishy]

I've ran and Undergravel filter in my 95 gal tank since I set it up 7 years ago. I originally did this because thats what we had when I was a kid (in the early 70's). It's only since then that I found many aquarists don't care for them. I ran it with a powerhead driving each draw tube. I also had 1 Whisper HOB filter.

That setup worked so-so for a few years but I didn't have much success keeping fish I wanted (long story).

After a few mistakes I started hanging out in forums like this and found out a golden rule (at least for FW): You cannot have to much filtration!

So I replaced my Whisper with 2 Marineland Emperor 400's and using some PVC pieces, changed the UG to reverse flow. This dramatically improved the water conditions in my tank. This is a planted tank and with the reverse flow, I don't have to worry too much about vacuuming the substrate and disturbing the plants.

Just a few months ago I removed one of the Marineland HOB's and installed a Marineland canister.

Fish, plants are doing well and the water is always crystal clear.

So in general I would say UG filters are a great addition when used with other filtration devices.