Snails have an upside and a downside depending on the variety. I've had tons of unwanteds come in on live plants.They definatly don't solve algae problems but do eat leftover foods. Currently I use Assassin Snails w/ my P's to clean up the unwanted snails. The best defense against algae is good surface agitation, fresh oxygenated water, no direct sunlight, no organic build up, and lighting control.