Help...Tropical Fish. To still keep a group of fish can i have one of each of the same kind? For eg...?

Yes, all types of tetra and danios will school together no matter what color. But the rule of thumb for a tank is one inch of fish per gallon so you don't want to go over that limit. The Pseudotropheus Demason though I've done some research and what I've read is that these fish are dwarf chiclids so putting them with community fish is not a good idea it's not the size of the tank that is the issue because they are dwarfs but these fish are extremely aggressive and should only be put in with other aggressive fish their size they would kill your tetra and danios. Also the issue of the difference in PH need between them wouldn't allow you to keep them together anyways because they are african chiclids they would need a higher PH. I think what you are talking about is a Khuli Loach?