It would seem impossible for water at normal operating temperature to be as high as you stated and have an acceptable pH and alkalinity. I have not seen tanks using both Kalkwasser and calcium generators with calcium levels maintained successfully in the 600 range. Water can only hold so much of an over saturation before spontaneous crystallization starts, which would mean a precipitation of calcium would start in the 500-550 levels at most. Your ionic levels would be way out of balance with calcium readings that high. Whereas your alkalinity is reasonable and your pH if I remember was OK. Such a high calcium readings could not possibly have been caused by water changes. As far as Instant Ocean Having a low Calcium level, that formulation was changed long ago and no containers of "low" calcium mix should be on the shelves. The problem was not a low calcium level, but was a low buffer level. Do not waste your money on ChemElite, just use a ferric iron compound like PhosLock, PhosBan, PhosaR or Drs. Foster and Smith store brand phosphate remover. You are already using charcoal. ChemElite is just a combination of phosphate remover, charcoal and an ion exchange resin at a much jacked up price from what they would cost separately and then combined. The ion exchange reins will not provide relief from the algae or "high Calcium levels". If you are doing water changes already the best additional practice would be phosphate remover as suggested by Biffer and increased circulation. If your pH is in line I would definately question the calcium tests especially if the test kit brand is the same and from the same source. It would take a whole lot of acid to get that much calcium (900 +) into your water. That would mean a VERY LOW pH or a LOT of CO2. Just what is your pH and salinity level.