Brand-new 10g- what to do with it?

One of my neighbors put in in our yard near the sidewalk. Naturally, being a growing fish keeper and having just seen Finding Dory just before I saw it, I took it inside. It had a "Free Hamster Cage" sign on it, but I want to use it for fish. I plan to sterilize it with some Hydrogen Peroxide or bleach solution before I use it. It will either go towards a new hamster or some fish. If it goes towards fish, what should I do with it? I wanna try multis- cichlids as they need 10 gallon for 2, some other fish, 2 male betas in a divided tank, a dwarf puffer, or...
I have 5 skirt tetras, 3 female betas, and 3 ottos in a 20 gallon high tank. The tetras and betas have had a difficult time getting along. IE fighting with each other when they're hungry.
So... split up the fish + new inhabitants for each, or some new fish?

 

I'd divide the 10 gal into halves, keep two of the female bettas, and rehome the third.

 

They have a strong hierarchy already, and it has been established that they are absolutely fine together. All the girls, or none in the 10.

 

Whatever you do, don't put a hamster in it! AI'm for 360 square inches at minimum.

If you do move the girls into the 10 keep an extra close eye on them because the upset of being moved and having to reestablish territories can change the dynamic.

 

Was it used for a hamster previously? I don't know if it's true, but I've heard that ammonia from the hamster urine can be absorbed into the silicone and leach into the water and cause a huge spike.

(It'd be an easy test though, just fill it, test it, and let it sit for a few days and then test again to see if it rises.)

 

20 gal long minimum and 5 minimum for betta sorority. Less than that can be problematic (and even that can be problematic!). It may be fine now, but I wouldn't expect that last forever.

 

Ok, little red. I'm not entirely sure, but it did come with a half used bedding and bag of food. My sorority has been working fine for almost a year. I think my curent girls might hurt a newcomer if I add more bettas. My altime plan is to keep the girls in the 20 and build it if I want and keep the tetras in a new 38 or 50 gallon tank when/if I can get it.

 

In another thread you mentioned that you got the girls in February. That's not "almost a year". That's not even 6 months!

 

No... I got MarcI on June 30 of last year. I got Sara and Zeebee on September 20ish of last year. The girls have all been in the same tank since September 24ish. The skirt tetras came on February 1. Sonic came March something, Stanley and Fleury came last week.

 

Well, I gave the tank to by brother for $15. PetSmart has a $-per-gallon sale soon, so I'm gonna use the money towards a 40 gallon breeder or a 55 gallon set up.