Barney

In my 120 Gal I have an under ground filter with 2 Power head pumps.
Do I need another filter?
I cannot use a cannister.

susitna-flower

Filtration depends on the number of fish and how and what you feed. Plecos, Oscars, Jack Dempseys, and other high waste producers require larger filters. Remember that a tank this size is MUCH harder to change, after it is established than a smaller tank.

Basically you do need more filtration.

Why can't you use a canister? Is there not room under the tank?
A canister holds the most media of any filter except maybe a sump. (even harder to hide)

Some people here on FISHLORE don't agree with using UGFs.
I use them, but with extreme care to clean the gravel, vacuum it, and use a "shop vac" on the up tubes every couple of weeks to suck any built up waste out from under the filter. My 125 gallon has an UGF, one powerhead and a 2028 Eheim canister filter.

The first choice for that size tank would be a canister. They are quiet, efficient and easier to clean than the UGF. One sized for the tank should process approx. 10 X the # of gallons / hour. for a 120 gallon tank that would be 1200 gph. Well, that is the rule of thumb, but most show just that they will accommodate a certain size tank. It is always a good idea to error on the side of more filtration.

IF you can't use a canister, then you will need 2 HOB filters, the largest you can find. Remember the 10 x the tank size / hour here because HOB filters don't have as much media capacity.

susitna-flower

Do you have your tank set up? Are you just in the planning stages, or do you already have fish?

At the top of this page click on the heading "Articles" There are a number of articles on everything from equipment to the nitrogen cycle, everything you need to know to set this tank up with the least problems. Also check out the fish profiles.

COBettaCouple

welcome to fishlore.

I'm not sure about UGFs, since we don't use them. What GPH do the power heads give you? You'll want 1200gph or more on that tank.

Trpimp147

i wouldnt suggest UGF if your fish dig then that will mess up the whole point of them creating an equeal suction. i would suggest buying 4 emporer 400s that will give you 1200gph

darkwolf29a

I'm not a fan of UGF, but I know people who swear by them.

Why can't you use a cannister? I have a Marineland for my 55 that takes up the same amount of room as a HOB filter, but does a better job cleaning. I also have an Eheim that out performs anything else I'm using.

My favorite filter setup, for big tanks, is a sponge filter and a cannister. Oh, and I overfilter BIG time. LOL I can't resist it, after setting up my Oscar tank. It's too easy to do, and doesn't cost much more.