I wouldn't put a betta in that tank at all; 10 gallons is too small a space to keep a betta with other fish. If a betta doesn't have room to get away from the other fish, they will become territorial and attack the other fish. A 20 long is the minimum recommended tank size for a betta community, and even then you will need a back up tank just for the betta.
Would you consider upgrading and keeping this 10 as a back up?
EDIT: Also, is the guppy a fancy guppy? Bettas can mistake the long fins and bright colors for another betta and be very aggressive toward the guppy.
A betta is not temperature compatible with your fish, and your aquarium is overstocked, so a betta won't be suitable for this tank. If you upgrade the neons and guppies to at least a 20 long, you could keep a betta in the 10.
Agreed with Flowingfins . You are already overstocked with the neons and guppies. Move the current fish to a bigger tank and put a nice betta in the 10. Could also add spme shrimp/ snails in with the betta but if not docile may eat them for lunch!
Also, even if you upgrade to a 20 gallon minimum and still decide to do a betta with other fish, there's no way for you to be able to tell at the store what kind of temperament it has. It's just a big coin toss which is why they're not recommended for a community tank.
Just gotta be lucky. Female betta is your best bet, but even than you gotta be lucky
Even females can be extremely aggressive, in my experience they can be more aggressive than males because they don't have heavy fins weighing them down.
And trying to be lucky can have disastrous consequences if you get the wrong Betta and it's not temperamentally able to live with the other fish and you don't have another tank to separate them.
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Ok thanks everyone!x My guppy is not a fancy tail. I would consider upgrading to a 20G or 36G Bow front if I could find a nice place for it.
Does anyone know if I can have 3 Guppies and 7Neons in this 10 gallon?'
EDIT: also does only having 1 guppy make room?
Neons are not suitable for a 10 gallon, they are active fish and need a 20 long minimum. You could have your 7 and 3 guppies in a 20 long though.
Only having one guppy and the 7 neons does not make enough room, your tank is severely overstocked as it is. Bettas and neon tetras are not tempersture compatible either. Bettas should be kept at 80 while neons should not go over 75.