Join Date: May 2011
Location: Elk Grove, California
Pond snails won't harm the bettas but they can and probably will nibble at the plants. If they're kept well-fed, this is less likely though.
A few pond snails here and there won't really do much to the bio-load. But if you suddenly find that you have hundreds, then you might experience an ammonia spike. If you do suddenly get a population boom, it could mean you are overfeeding the tank because well-fed snails breed more.
Easiest way to get rid of them is to remove them manually as you find them and uh . . . squish them. Put them between paper towels or newspaper so you don't have to see the squish results. Also be on the look out for egg sacs, gelatinous masses attached to plants decor, tank walls . . . pretty much anywhere. Remove the eggs and there will be no baby snails. You can also control them with assassin snails which also wouldn't affect your bioload much either. You would want maybe 2-3 assassins for your tank. Not all assassins do a very good job of snail eating though. Both Laki and I have had experiences with assassins that refused to eat snails. Hers eventually did, after a couple months, but mine just flatout died.
Easiest way to get rid of snails during a QT is potassium permanganate. Some local fish stores may carry it or I've been told you can find it in the water purification aisle at hardware stores like Lowe's. It's 10mg per gallon for 10 minutes. You can also use Jungle Labs Clear Water at double strength. This also takes care of external parasites and some bacteria.
If your bettas attack or eat them, let them. It'll keep the snail population down, provide your bettas with amusement, and if they eat them, give them a nice snack. :)
The pro of pond snails is that they eat up any leftover food. If you're usually very careful about not overfeeding your tank, then you probably don't need them. If they don't have enough to eat, they go for the plants.