What calcium supplement are you using? and how are you adding this?
(please tell me you are doing it with your top ups and not directly to
the tank). 500 seems a little high - I would think you should be aiming
for 400.....another question would be how much coralline algae do you
have? (the red/purple stuff on your rocks and glass) - this also uses
calcium....

Gill

Gill,
To answer the other part of your question, there's not much coralline
algae at this point...the tank is only around 2, 2 and a half months
old or thereabouts. The green hair algae has just hit the point where
it's stopped growing

Mitch