what I usually do if I get the green algae on the surface of the potting mix- is get an ordinary table fork and fork it over lightly- usually this does the trick, if you leave it and dont do it-it will eventualy choke the plants and restrict their root breathing and airiation,
It is particularly noticable on all spagnum moss peat mixes- that have been watered withg a liquid seaweed mix.
