A word of warning about snails...
A friend gave me spare weed to help keep my pond water healthy. The generous soul also included some pointy-shelled snails, which ate debris and growing plants alike! :'(
It took me a while to remove them all, leaving the dark, disc-shaped snails that don't appear to do any harm at all to genuinely healthy growth. The pond plants recovered eventually. Sorry I can't give you the biological names of the offending snails - just be careful! :)
