high alk, low Ca. How can I fix this?

[reefkeeper]

Presently I am having a lot of trouble keeping the Ca levels up in my tank. The alk was also a bit low, so I replaced my reactor media (ARM) and turned it up a bit. I also used some commercial buffer. I now have a DKH of 14.5 and have struggled to get the calcium to 330ppm. Specific gravity is at 1.026 and magnesium 1170ppm. What should I do to correct the Ca levels?

 

[randy holmes-farley]

You need to add calcium with an additive that adds only calcium and no alkalinity. So you cannot use a reactor, limewater, or both parts of a two part additive to solve this problem. I'd suggest using calcium chloride until the calcium is about 420 ppm. It will take quite a lot compared to the usual manufacturers dosage.

 

[reefkeeper]

This morning I added 10 teaspoons of CACL (255 gal of water in my system). I waited about 2 hours and retested. The Ca went up 4ppm. I had calculated it should have gone up 20ppm. Am I doing somthing wrong or should I just increase the amount ?

 

[randy holmes-farley]

How did you calculate that?

 

[reefkeeper]

I used the calculator on Andys SPS aquarium page.

 

[randy holmes-farley]

OK, Andy's calculator only calculates how much went into the water. If alkalinity is high and you precipitate some of the calcium as CaCO3, then the alkalinity will drop and the calcium will rise, but not as much as that calculator suggests. So it is a useful guide, but in cases of high alkalinity, you'll have to add more.

 

[randy holmes-farley]

Also, unless you are using the exact material that Habib used to determine the amount of calcium in a teaspoon, your results will vary. You may have used an anhydrous material (like Kent's Turbo calcium), or something else, which may have more or less calcium per teaspoon.