odd calcium/alk issue

[crawlerman]

My water was maintaining 1380 mag, 8.5 alk and 550 calcium. My alk has dropped to 7. I was maintaining 8.5 with one cap of Kent Marine Pro dkh buffer per 5 gal top off. I am now adding three caps per 5 gallon (ATO) and my alk remains 7.0. I have not added calcium and haven't done a water change in 2 months but my calcium is at 560 and has not dropped. My thought was to keep dosing alk and let calcium fall naturally to balance, but calcium won't drop and alk won't go up. Calcium tested with new red sea kit and verified with API, Alk tested with seachem and verified with API, Mag tested with red sea. Using reef crystals. this would make sense to me if my mag was low, but I don't think 1380 is low. Lost 2 maricultured acro colonies and a blue tort frag in the last week to STN. What is my best course of action? I'm thinking 2, 20% water changes per week with a lower calcium salt. I don't want alk to swing too much with acros already stressed.

 

[bertoni]

That calcium level should be safe enough, even for the long haul. How big is the tank? I'm not sure how much is in a capful, but that sounds like a very low consumption rate. Many tanks consume 2-3 dKH per day. The consumption rate is 2.8 dKH per 20 ppm of calcium.

 

[crawlerman]

It's a 180 mixed reef, but the sps are all small frags. Cap is about 1.5 tablespoons. 5 gallons lasts 3 days. Up until about 2 months ago the cap was enough. I did add about 15 frags mid february, so maybe that's it. Just seemed off that I keep increasing buffer with no effect on alk level. Also thought it was odd that the calcium didn't drop at all in that time. I guess I was thinking the high calcium was keeping alk low, but I don't think it works that way. Low mag would make sense but the test kit is newer. Is there a better buffer to use or is the Kent fine?

 

[nereefpat]

I bet you just need to add more alk. I can't find much detail on the product you're using.

Baking soda dissolved in RO water is cheap and works well. Here is a calculator to play around with: http://reef.diesyst.com/chemcalc/chemcalc.html

It looks like for your system, about 4 teaspoons of baking soda to raise 1 dKH, but don't add it add at once.

 

[crawlerman]

I guess I'll just keep testing and bumping it up. This is the product I use https://www.kentmarine.com/products/kent-probuffer-dkh.htm

 

[nereefpat]

I did find that. I just don't see anywhere that tells you X mL will raise Y dKH in Z gallons.

 

[bertoni]

I suspect that the consumption rate of alkalinity is low enough that the calcium will stay high indefinitely. You could measure the alkalinity each day or so for a while, to get a trend line, if you stopped all the dosing for a bit.