what do you think about undergravel filters?

If you are willing to do the upkeep, they are good. If you aren't they can be deadly. A powerhead and filter should cost $35-50.

I have U/G filters on several of my tanks. They are great reliable bio-filters, providing a substantial back-up should your other filter "crash". Cleaning is not difficult if one has the correct equipment. Most important is a reliable siphon. People that do not understand the mechanics of substrate vacuuming are usually the most vocal complainers, but the substrate requires vacuuming whether there is a filter plate beneath it or not. There are two methods of powering U/G filters, either air-lift or power head. Power heads are best in larger tanks while the air lift type works best for smaller tanks and nursery type tanks. Both perform equally well. Shop around and look at some of the different types available. I think for your 55 a two plate system with two small power heads would be the best. One note, if you are going to keep cichlids that like to dig (African Rift Lake, Oscars, Geophagus) they will constantly be uncovering the plates and requiring gravel grooming. There are ways to make this work also (extra plates or screens between the gravel surface and the U/G plate) just another layer of tinkering. Also if a planted tank is in your future make provisions for keeping the plants in separate containers instead of in the actual substrate. These are a few of the considerations involved in U/G technology. Bottom line, they've been around for years and they do a great job. Hope you find this helpful.

its a biological filtration so i reccomend you to get one.

1) Undergravel filters (UGF) are excellent biological filters. The smaller the size of thegravel, the more surface area for bacteria to live on.

2) UGFs CAN be excellent mechanical filters (removing particulates), but it all depends on the gravel you choose, and how much there is.

Here’s how it works:

Think of gravel sizes in opposites: the size of BB and Marbles. If you used gravel the size of marbles, there are big passageways between the marbles so any solids will probably all go through.

On the other hand, if your gravel is the size of BBs the open space between pieces is much smaller, so more particles can get caught. And the thicker the layer, the longer the particulate is in contact with the filter media and the more chances it has to get caught on the gravel. But the gravel particles can’t be too small or they will fall through the opening of the UGF and plug up the whole thing.

Filtration quality is ALL about retention time in the filter media. The UGF flow rate is slow but has a long retention time. Comparatively, the power filter flow rate is high so the water passes through it more frequently, but has a low retention time (just a small, relatively thin pad)

When a filter gets plugged up it’s called being “blinded”. Gravel has so much space it takes a long time to blind it. However, a small filter can be plugged up very quickly if the is a sudden increase in particulates from cleaning.

I have both, each has it’s place. Generally:

UGF:

Pros: No need to buy replacement filter media, gravel is cheap, plastic airstone is cheap

Cons: Cleaning the gravel

HOB Filers

Pros: Very easy to replace media

Cons: You have to buy more media, the bottom of the tank will still need to be cleaned

The initial cost of plates, riser tubes, airline, airstone, gravel, air pump is going to be a bit more than 2 HOB filters (you may want 2 because of the shape of the tank.), but not by much.

Note: if you go for a UGF I recommend against the "Marina 200" air pump when you are shopping. It's got a bad design on the dual-output. I had 4 break in a very short time. I've had much better experience with "PennPlax AirTech 2K4".

I love undergravel filters, but only when used with a powerhead, not a pump. To start a 55 gallon tank you're looking at at least 100 bucks (not including fish or heater, or gravel). You want about 3 inches of gravel for the filter to work best. So you're looking between 70-90 pounds for a tank that size.

they work good, i had one in my 55g and it kept my tank looking clean evryday, they dont cost that much, the most youll spend on one is no more than 30bucks, the draw back is cleaning it, i cleaned mined for the forst time and i took it off because it just created a big mess

They can be alot of trouble and don't work very well. I would get a HOB (hang on back) filter as they work so much better than a UGF but for a tank that size i'd look into a canister filter if you got the cash, if not buy an Aquaclear 110 and re-use the media filter and bio balls. Works much better and has room for many options..

Well, they work good. But, it can be a pain to clean them out. you also have to replace the air stone every so often. Usually, an under-gravel filter, can't just "filter" by itself, you would need a power-head (over-the-back filter) as well, to keep all of the beneficial bacteria.

EDIT: Oh, a 55 gallon?? No, you might want to avoid under gravel filter, and go for something more suitable.

under gravel filters are best when used also with one of the waterfall ones that sit on the back. Things to price for the tank are waterfall filter, pump for the under gravel, air pump, gravel, gravel vacuum, plants, decorations, and water conditioner. Once the initial cost is over its not bad to maintain.