I've heard you're not supposed to have more than one mature fish per gallon of water, but it really depends on the fish.

A lot also has to do with whether or not your tank (filter media) has gone through the Nitrogen Cycle. Always start with one, cheap fish, with a new filter and monitor the ammonia and nitrites.

I have very mixed feelings about UG filters, even with power heads. They do encourage deep root growth in plants, but are also biological time bombs, just waiting to go off.

Yes, by all means, get a power filter; the bigger the better. Always use a filter rated for 2 -3 times the advertised gal. capacity and if you insist on using a UG, always draw from the uplift tubes when you water change, to remove as much of the excess gunk trapped under the plate as possible.

However, regardless of your filtration, never forget that an aquarium is a closed system. Pros with large breeding set-ups keep them healthy with a filtration system than adds fresh water continually.

I first kept tropicals back when the latest in filtration was an air driven siphon filter and as much as I appreciate the efficient power filters now on the market, I fear they have given too many people a false sense of security.

In the old days, water changes were our only means of keeping our fish healthy, but now, the ads for filters seem to be giving the impression that they replace that need, and nothing could be further from the truth.

The plecostomus is going to get BIG--will eventually be about 8-10''and wreak havoc on your plants. They're gentle but too big for most modestly-sized tanks so they uproot plants. (Did you know that they need algae wafers and will come for them as soon as you drop them in.) Anyway, keep the pleco's size in mind when calculating your fish load.

The danio should have other danios with him--they are a schooling species. They tend to nip fins of fish like gouramis when alone. Also they are much livelier in a group of half a dozen--very lonely by themselves.

Personally, I love my Hagen Aquaclear filter--so easy to monitor and clean. You can change the filter media easily and they are very reliable. Just hangs on the side or back of the tank so very accessible. UG's are tricky to maintain, especially if you have a big fish like a pleco.

Good luck.

My dad owned a petshop aways back and installed UG filters in all tanks. They seemed to work for awhile, but then slowly became ineffective. I read literature about the occasional need for backflushing them. In our artificial environments, while bio-chemical action is good, it really needs to be supplemented with manual cleaning, partialy through the canister filters/ filter media, and partially through water changes / siphoning, to remove solid wastes.