I need fish help!

[Dakotah]

First let me say, I am not a fish person, I know they are pretty and I know what a goldfish and a betta is and that's about it as far as "pet" fish go

So as yall know TJ's dad moved to FL.
Well he had a fish tank and TJ & I got it.

Its about a 30-ish gallon tank (it could be bigger but I can't tell lol) and we have one of those algae cleaner fish that is about 10 inches long, a red tailed black shark that is about 2.5 inches long, plus there are about 5 little minnows.

TJ's dad has had these fish forever lol

But TJ and I are thinking about adding another colorful fish. But we don't know what would go with this combo?
The shark can be a little mean, but I have only seen him/her be mean twice in almost 7 months but I think she/he might be PMSing cause I don't know if its a male or female lol

So help me!

*MODS: I think this might be in the wrong place so please place it elsewhere if need be *