Low calcium

[Reefer35]

Ive had my reef tank for about 9 months. It's the third tank I've had over the years, all sps previously. For some reason I cannot get the calcium up. Its a 40 breeder and I dose with c balance. pH is 8.4 with a dkh of 12. My calcium tests between 340 and 360. Also this particular tank has not been stocked with any stoney corals. The Monti cap and acro that I did introduce died within 6 weeks. Currently there is only a small Duncan. Any help would be appreciated. Thanks

[xmas_one]

Sounds like you are dosing too much alk and not enough calcium. I’m assuming you balanced your levels before you started your 2 part dosing regimen? Do you have a doser or are you dosing manual? 12 dkh is way high IMO, you should be shooting for around 8. 

http://reefkeeping.com/issues/2006-02/rhf/index.php

[Gil&Fin]

Here's an oldie-but-goodie, too.

http://www.advancedaquarist.com/2002/11/chemistry

 

[Reefer35]

Thank you very much for the replies. They are both helpful.

[Jeremevans]

I'm a big fan of that that article. Figuring out which zone you are in is a big step in understanding the right action to take. 

Something that I think is mentioned in the article, but might be worth reiterating is that magnesium levels can be important. If you have low magnesium and try to raise calcium you might have some frustration. I think the rule of thumb is that you need about 3:1 magnesium to calcium or the calcium can precipitate out as calcium carbonate.