One filter or two, on a 55-gallon long?

I believe it is better to have two heaters and two filters in larger tanks. 55 is not large enough to make a big difference, but it couldn't hurt either.

I have a pair of Hagen AquaClear 70's on my 125 and a pair of 300 watt Rena Cal Excel heater, simply because I need 600 watts to warm this tank and I don't know of any heater over 400 watts.

I don't think you are agitating the surface of the water enough for a 55 gallon aquarium using a single Penguin 350. I've got two 55 gallon tanks and both include an undergravel filter setup with two power heads on each side of the tank. I also use the air tube into the power heads to increase the oxygen flow in the tank. The power heads help circulate water through your gravel bed where I recommend using BioZyme to create a good bacteria base to breakdown fish waste and excess food. If you had those in the tank, the bio-wheel filter would probably be adequate, otherwise I'd add another external filter or even a sump pump that pushes water into a box on top of your tank with bio-balls and some sponges.

Given the cost of fish, don't go cheap on filters.

I started with the same set up, a 55 gallon and a Penguin 350. I wasn't happy with the filteration and got another Penguin 350 for the tank. This works wonderfully. I would say maybe get a Penguin 200 and put it on the other side, although your 350 will be plenty if your tank isn't over-stocked. They say one inch of fish per gallon is a way to determine how many fish to keep.

That one filter is probably fine but two is a good idea just in case something happens to the first one. You could even get a small cheaper filter for the other side of your tank. I had a 55 gallon with one filter that was equivilent to yours plus a Whisper for about a 15 gallon tank. The water was clear and I never had any problems. The smaller filter is good as a back up if you have a big fish die and block your filter.

I think the two-filter idea is great. I have an Eheim 2213 canister for my 55 gallon (it's supposed to work for tanks up to 55 gallons, and most of what few fish I have are small), plus a power filter on the other side, also for a 55 gallon tank. I'm very happy with this setup. It's convenient especially when you want to clean one of the filters and not have to worry about recycling/establishing bacteria on the media.

The way i look at it the more the better. I have a 120gal saltwater reef. my filtration is rated for up too 500 gal. my tank is so clean. adding another filter will also add more current to your tank. i find that most freshwater tanks lack water movement which is vital for the fishies. I'd buy another filter. have you thought about a canister filter or even a sump? these would be great additions to any tank

I had a 55 g long tank with chiclids in it, with the same filter you have described on it. It cleaned the tank well, but i had to change the filters often. It would not hurt to get an extra pump on the other side.

must have the undergravel filter out. you are able to purchase 3 foot sections of tubing from maximum petco, petsmart or internet puppy shops like Dr Foster & Smith. because of it really is length a fifty 5 gallon tank is difficult to effectively filter out with merely one filter out. Congrats and strong success !

I always like using 2 filters rather than 1. That way you know for sure that there is sufficient water movement at all areas of the tank. And if a filter dies, at least you still have 1 filter going so your fish don't all die before you can get a new one.

Try placing it in the center of the tank if you can or if you want you can get another filter but if it says up to 75 gal. then it should be fine but it's all up to you.