Snail species
Pond snails - These are the ones that are most common. These little guys will multiply and be all over your tanks. Most of the time, they are introduced by riding on plants. I found some of these snails eating my plants. They only ate softer leaved types of plants but regardless, they ate my plants. They stay small and leave jelly like egg sacks on plants and glass.

Ramshorn - These snails are the second most common found in the aquarium, and they reproduce like the pond snail. Just like the pond snail, they are a pest and will reproduce quickly. I have also seen these eating the same plants as the pond snails.

Nerite snails - These DO NOT reproduce in fresh water. They will eat algae off the glass and make your glass look clean. I always have these in my tanks. You can find them on the internet for about a $1-2 a piece. They get about the size of a nickel, and are green to black in color. There are different varieties of nerite snails, but olive being the most common.

Apple snails - These are the ones that are sold at petsmart, petco, and your LFS under the name mystery snail. There are different types of apple snails, some eat plants and some eat the dead plants. I have some of these in my tanks and they look cool and eat dead plants FAST. They get big (larger than a quarter). I have Pomacea bridgesii in my tanks, which only eat dead plants. Make sure you dont get the any other species. Check out http://www.applesnail.net/ for more information and the different species.

Malaysian trumpet snail (MTS) - These snails eat dead decaying matter and they borrow in your substrate. They will reproduce quickly and are not bad in for your planted tank. These guys will help keep your substrate aerated and little pieces of food from going to the bottom of the tank.

Assassin snails - These guys eat other snails. Yes, they hunt down and eat all other snails. Not much is known about these except that they are somewhat rare and cost anywhere from $5-15 each.

To rid your tank of snails
There are a few ways to do this:
1. Place a piece of cucumber in your tank. Once the snails cover the cucumber, remove it along with all the snails. This will not totally remove all the snails in the tank, but it will reduce their numbers. Keep repeating everyday until no more snails are eating the cucumber. Remember to place a fresh slice of cucumber in each time.
2. Starve them. Stop feeding for as long as you can. They WILL die off eventually. If you do feed, remove ALL leftovers. i think this is the best way to removing snails. It might take a couple of weeks but it will work.
3. Manual removal. Pick them out when you see them.
4. Snail eating fish. Since you probably have a piranha in the tank, this will be hard. You will have to move the piranha to a different tank for a while. Clown loaches usually take care of snails pretty fast.
5. Assassin snails. Get a few of them and watch them eradicate the other snails. Sell them when you are done.
DO NOT use chemicals unless you are going to tear down and wash the entire tank out after you add the chemical.
Snail prevention
The best way to stop snails, is to make sure they dont enter your tank in the first place. The good snails (Nerites, etc.) will be put in with your knowledge so those you dont have to worry about.
Wash your plants in warm salt water before putting them in your tank. This should kill all the snail eggs.
This post has been edited by maknwar: 23 August 2009 - 07:19 PM