Aquarium snails: which to choose and why they multiply

Snails carry a bad reputation that is rarely theirs. When a tank fills up with snails the problem is not the snails: it is leftover food. A population only grows as far as the available food allows, so an explosion of Physa or Planorbarius is a useful symptom rather than a plague: it is telling you that you are overfeeding.

They do not all do the same job, and choosing well changes the outcome. Melanoides live buried and turn the substrate over, which stops it compacting. Neritina and Clithon are the best against hard algae on the glass and have a little-known advantage: they do not reproduce in fresh water, because their larvae need brackish water, so they never multiply. The exception is the apple snail (Pomacea), large and striking but which does eat tender plants.

They need minerals in the water for their shell. In very soft or acidic water the shell erodes and pits and worn edges appear: that is not a disease, it is a lack of calcium. And like shrimp, they die from copper — including the copper in the products sold precisely to remove them.