For: Algae - Rocks & Glass
Recommended per tank:
1 per gallon of tank to start
Example: 75g tank = 75 Astreas
This is a "rule of thumb", not an exact science. You can add them all at once or add to your population as you can until you reach this approximate number. Over time they will naturally decrease in numbers. Try to keep 1/2 of the starting number in stock going forward.
Average size is 1/2-1 inch. Astrea snails are fantastic algae eaters being quite at home on your rock or glass. They are slower yet more thorough cleaners allowing coraline to take over where they've been. Other "turbo" type snails aren't as thorough & can topple corals & rocks when larger because they are very strong. Only downside to Astreas is that they can't right themselves when toppled upside down. You must flip them right-side-up or they will die...then they'll go on their merry way. :0) The recommended numbers are needed to be effective in cleaning.
Astrea Snails need to be placed on their foot after acclimation or they can die. Note the bottom of their shell is round except for a small flat spot on the round where their foot comes out of the shell. You need to place that flat spot against the glass - tank side & back walls are best.
Pictures are examples only. Expect some variations.