I have had a total of 3 nerites for my small tanks. I think you really don't need that many because they just munch through the algae and they will hunt for more. I just drop mine in. If you have water that is deficient in minerals, you will probably need to add some calcium to keep their shells hard. I read somewhere online that you could crush some egg shells and run that in your filter and it'll decompose and release calcium for them into the water. If you end up getting more than one snail and you start seeing all these little white dots, they are trying to reproduce but they need brackish water to do so. I separated mine lol.