What can I keep with a betta?

I've got mine in a 15gallon with guppies and a small siamese algae eater. They all get a long just fine. He even leaves my baby guppies alone It's a planted tank and I find him all jammed into different nooks and crannies around the plants.
 
A few suggestions that won't work: You shouldn't put an otto in a new tank. They are compatible and don't get very big, but they eat algae pretty much exclusively and can easily starve to death in the midst of plenty in a new tank that doesn't have algae yet. They are also social fish so you would need a small group.

Danios and the genetically engineered glofish need more space than a ten because they like to swim fast and they are schoolers. You need 6.

Mollies are brackish water fish and though they can be kept in fresh water they are very prone to infection when they are.

Now, the things that would work:

3 or 4 cories would really liven the place up. They are social fish so get the group.

OR a school of 10 neons OR 10 cardinals OR 10 ember tetras OR 6 cherry barbs. There are other tetras that would work also as long as they are small and non nippy. Platies would be fine. You could have 3 or 4.

If you go for guppies, get females. It is possible that a betta will see the males flowing fins as a challenge, I have heard, but I must admit I have never seen it be an issue.
 
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