[welcome]
This is an OK place to ask, but the chemistry forum is better:
http://reefcentral.com/forums/forumd...s=&forumid=112
I do not remove the sludge very often (once a year maybe). I usually add new calcium hydroxide whenever I refill it with water (I now use 2 x 44 gallon trash cans connected together). Sometimes i try to get more out of the sludge and don't refill with calcium hydroxide, but I always check the conductivity to make sure the potency is adequate.