IME and IMO, a five is too small for anything but a Betta and one Mystery Snail. More Mystery Snails are fine if you are an experienced enough keeper to recognize if things are going south for the snails. And you must supplement feed; especially calcium. And they not only do not eat poop, they create a great deal of it so frequent water changes with substrate vacuum are a must.
Shrimp are inappropriate unless the tank is at least two months past cycling and so heavily planted you cannot see your Betta by just glancing at the tank. Shrimp are extremely sensitive to parameter changes so frequent, small water changes are most important; without enough planting they will stress and become compromised. I know, people will give testimony they are doing so but you should be able to brag you've had shrimp in an inappropriate habitat for years; not just a few weeks or a month or two.
The only other fish that would work in a five require specialized care and live and frozen food. No shoaling variety will work if kept in a proper shoal of at least six. Also keep in mind a five gallon tank only holds a bit over three gallons of water once you account for decor, substrate and equipment.
I always advise a back-up plan whenever one is considering tank mates. Even Mystery Snails can have there eye stalks removed by an overly aggressive Betta. There are plenty of post about it on this Forum or if one Googles.
Finally, tank makes are for us; not the Betta. They remain healthy and active without them. If you really want tank mates other than a Mystery Snail, go up to at least a 10 gallon.
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Last edited by RussellTheShihTzu; 02-23-2019 at 06:19 PM.