I need fish help!

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 :lol-sign:

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 *

Adult rainbow fish. They're one of my favorite underused freshwater fish. They get along with just about everything and are very hardy. Downside - they do cost a bit

I've always like guppies they are pretty!

Do you know what water parameters your tank has (hardness, pH etc)? Temperature? Also could you get the L x W x H? (there are 7.48 gallons to a cubic foot).

If it's 30 gallons, it may be at capacity already. (the shark and pleco grow larger)

Oh I like those!

I like the name guppies, so that is why I would get one lol

I really don't know the parameters lol
The shark hasn't grown in almost 2 years and neither has the algae eater. There is quite a bit of room in that tank though.

Those red tailed sharks, I always found to be rather non-aggressive. Hmmm. Well, it is always best to add the ones that tend toward aggressiveness last so they're the new comers. I think guppies are great, also pladdys. They have red ones with black tails and other colors. I had one that was super aggressive when she was about to have babies, but otherwise, they're typically not. Mollys are sometimes a little aggressive. But those black ones are sure striking. I'd try them later. But they are prone to disease more than many. Gourmies are beautiful, but again tending toward aggressiveness. Swordtails too...just gorgeous, but really ornery. lol. Just add one or two at a time for a while. I'd recommend fancy guppies or pladdys to start. Or better yet, ask the fish store person if he/she is knowledgeable. Have enough plants in there so the fish can hide when they want to. I love the little cardinal tetras. They're hard to get these days, so neons would be nice. A lot of the tetras are gorgeous. They really love to swim in schools especially, so you need probably 4 or 5 at least, for them to be really happy. One inch of fish per gallon of water is a good rule of thumb for most small community fish. If I think of anything else, I'll pipe back up. Good luck. Aquariums are loads of fun, albeit work.

I would avoid guppies if your shark is on the aggressive size (by the way they are known for being somewhat aggressive, so avoid small fish and slow ones with long fins). Rainbow fish are totally awesome but as mentioned, expensive. Plus, you need to get a small school, you can't get just one.

It's not hard to figure out how big your tank is. Measure the length, width and height and google tank size calculator. It should be able to tell you how many gallons you have. This is important to know because you really shouldn't be adding many more fish if you don't know how big it is, plus if you have a common pleco your tank is really too small for him and bordering on too small for your RTBS. They should ideally have 40-50 gallons.

Oh ok.

Well TJ's brother has a 50 gallon tank that he said he would give us, if we decide to get more fish.
He said that the tank we have now should not have anymore fish in it, but if we wanted to get another fish he has a 50 gallon tank and a 60 gallon tank he can give us.