That is alot of fish for a small tank.
The general advice I picked up from here is that a tank should be scrubbed with a scrubber with no soap just to get the "stuff" off the walls.
And having a aquarium vaccum hose to syphone the stuff off the rocks on the bottom is a good idea as well.
And how many fish for a tank is found by findin out exactly how big the fish are supposed to be when all grown up and then having one gallon of water for every inch of fish.
So, if I have a 1.5 inch betta with three zebra that are roughly 0.5 inch.
0.5(3)+1.5=3.0
That's 3 inches of fish so my tank should be atleast 3 gallons.
There are lots of great books on fish keepin at the library.
BB