Choosing fish for small tank with a betta.

[silentskream]

why dont you fill the tank all the way up so you can use all 20 gallons?

 

[amanda_]

Kuhli loaches like to be kept in groups, so its a good idea to have at least 3. They love hiding places and plant cover and don't usually get much larger than 4" so I think your tank will be just fine. However, they prefer soft water with a low pH ranging from mid 6 to 7. They can be acclimated to harder water but their lifespan will be cut short.

BB gobies are brackish water. While some may tolerate fresh water, their lifespan will be much shorter.