I wouldn't attempt it in your set up. Skirt tetras are known to be fin nippers and in such low numbers (same with the other tetras) they will be prone to fin nipping and all around rambunctious behavior. Which isn't good for a slow moving big finned Betta.

They can be kept with other tetras and other fish. I've kept them with Cardinals, ember tetras, platies, Otos, cherry barbs, Harlequin rasboras, and Cories. It all really comes down to the personality of the Betta in the end. Some can be quite peaceful and others can be quite aggressive.

Maybe if you only had a school of 6 Phantom tetras or a school of 6 Bleeding heart tetras in the tank then you could try to add a Betta. Tetras are schooling fish and are usually found in the wild in schools of hundreds. And usually when they're kept in low numbers it leads to fin nipping.

I've never had Phantom tetras so I don't know where they stand on the fin nipping scale or compatibility, but I do believe Bleeding hearts can coexist.

Personally I'd just stick with a school of one tetra and have six of them and return the other five. They'd be much happier. And possibly then you could add a Betta (depending on the type of tetra). There's not a lot you can do with a 15 gal and even less you can do with a tall one.

Aqadvisor is a good website that can show how full your tank is and how good your filtration is and compatibility. It doesn't though take in the benefit of live plants. It's not 100% right all the time, but is a very good resource.

You could always get another tank and set one up just for the Betta....five gallons aren't too expensive.... ;)

Thank you for the detailed answer! I'm always thinking about returning the other few and sticking to one, but the stores I bought them from won't do fish returns, which kind of stinks. I'd love to have a school of Phantoms or White skirts, I think they're beautiful (I love my diamonds too but, there's always a preference haha) And you're right about the 5 gallon tank, I actually have one not set up, and I was actually debating to get it running again but between my plants and my other hobbies, my room will swallow me up! Thanks again

Oh yes Diamond tetras! I don't know why I kept typing Bleeding heart tetra, they don't even sound remotely the same.

I'm trying to choose a type of tetra for my 20 gal and phantoms, diamonds and white skirts were all on my list. I think though I'm going to try and find some emperor tetras....

Good luck with your tank!

emperor and diamond tetras are both beautiful fish. these two don't seem to lose their beauty as they age whereas some fishes colors tend to fade.

fwiw, i had a 5 gal. tank with a male beta and 3 cherry barbs housed together. the betta started out with some posturing but soon found out he could not keep up with the speedy barbs and they lived peacefully afterwards.