Less than 6 neons will hide a lot in the back of the aquarium and act weird. Neons like slightly acidic and soft water. Good water quality is a must. The thing about neons is that they often get neon tetra disease, its really a plague right now and there is no cure. I have never had much luck with neons, I don't know why and I know a lot of people who get disillusioned with them. The much prefered alternative are the cardinal tetras. They look like neons but have more red and blue coloring and are bigger. Cardinal tetras are one of the most colorful fish u will find in freshwater. They are more expensive than neons (not by much) and are usually wild caught. Because they are wild-caught, they need more acidic water than neons, like 6.5. I find that after the initial adaption phase, cadinals do great with with even 7.0 PH. Also, I have noticed that my cardinals seek "friends" unlike what I have seen with neons. My cardinals school with my rummy-nose tetras and use them as big brothers to protect them.