Im have alk problems.

[BCOrchidGuy]

Murray, I don't want to say you are wrong because obviously you aren't. What Bev wrote is acurate for the most part though. Yes there will be systems that just do fine on water changes but for the most part the Ca, Mg etc etc in salts will be used up in a very short period of time. Types of corals you keep, additives, light, temp all will play a role in how quickly Ca is used up and of course frequency of water changes will play a role as well. God knows I'm no expert, I've scratched my head so many times over reef chemistry I'm surprised I don't have a bald spot.

Doug