I have taken bags of gravel from torn down tanks, dried it, sealed in a bag for like 6 month, washed with hot hot water, put in a tank and out comes snails inside of 5 minutes in the tank. lol. They are pesky little things but I like them. They eat left over food, they eat dying leaves, they clean the glass of anything, and are a good little clean up crew. If one week you see 6 snails and then next week, 600, you are overfeeding, so they are a great indicator for that as well. They breed when food is good, go dormant when it's not, so population explosions are usually always related to too much food.
20g platy, , 2 x 10g shrimp, 3 x 20g shrimp, 7.5g shrimp and 1 great dane/mastiff puppy.
Sump Pimp #2
My Tanks and my shrimps