red-tail sharkrainbow shark

Hey everyone, my name is Jae! I'm new here and I'm a (sorta) new fish owner. I've been mostly keeping Bettas (3 in 10-15g tanks), but I have one community tank (15g) with cories, shrimp, and neon/ember tetras; so a total of four active tanks. I've run into a bit of a dilemma and I was looking...

I have one red-tail shark and one rainbow shark now, I used to have 3 of each before I knew you weren't supposed to keep multiples of them. They used to be swimming on all levels of my tank posturing to each other, but now since there is only on of each I only see them during feeding time. They...