An infestation of small snails can be eradicated, or at least very heavily reduced & well controlled/ kept in check, by using some Flourish Excel in the recommended dosage on the bottle. Metricide also works extremely well, but one must be somewhat careful with it - it has double the strength of excel (so use 1/2 the dosage) & slightly different overall properties. Try excel, it has given me great results with removing snails & it does wonders at reducing/almost eliminating algae in a planted tank.
Try it.
Paul
Try it.
Paul