how many snails are too many

As some of you know i started my tank 1/15/09 and everything is still good. About 10 days ago i started noticing tiny-tiny snail like creatures crawling all over the glass. every night there were more and more of them. About 3 days ago big ones started coming out as well(1.5in long). I did some research and found out that they were stomatella snails and that they were benificial to the tank. As of last night there were probably 50 small ones and about 15 big ones and those numbers increase drastically every night. I have notice some of the big ones getting to a high spot in the tank spraying smoke like stuff in the water. should i do something about this or not

 

The smoke like stuff is sperm/eggs. It's them mating basically.
There will only be as many as the tank can support

 

one of my friends saw them and wants to by some off of me. if i gave him 20 would be ok.

 

+1

Like most of the CUC critters, their numbers keep a natural equilibrium with the amount of food in the tank.