Originally Posted by Sena Hansler
Ig you are going to have 10 neons with a betta... I defintiely do not recommend just adding a bigger filter. They need room - as they are super active and this can severely stress out a betta.
Actually Neon Tetras can be housed safely and thrive in a tank that's only 11 gallons (base footprint of 18" x 12", while a standard 10 gallon's base footprint is 20" x 10", there's only a slight difference), see here
. With that being said, yes when it comes to Bettas skittish and active fish may stress out your Betta, but then again it depends on the Betta itself, my Plakat boy had no issues with the Rummynose Tetras and they're an active bunch, along with being a tight schooling fish, I saw no problems.
Also bumping up numbers reduces the chance for fin nipping, six is the minimum but preferably groups of ten and up is the best. Upgrading the filter will help tremendously, or if you can't upgrade your filter (and I'm assuming this is a three stage filter like AquaClear filters), you can cut the sponge in half and remove the activated carbon, and put in more biological filtration, this will also have the same effect as upgrading to a 20 gallon filter.