Alkalinity question

dirtdobber06 · Jul 28, 2015

120 gallon tank, 10 gallon fuge, and about 10 gallons in sump. Borate alkalinity 0.05, total alkalinity 2.5, Calcium 450, Mg 1375. I have added Baking soda several times (3 teaspoons dissolved into fresh water and dripped in slowly with IV bag). I notice the Alkalinity/pH will rise but eventually comes back down. My tank seems to be consuming carbonate but not so much on calcium. I also recently started dosing vinegar because I have a lot of algae in DT. I am trying to get my calcium and alkalinity into the range shown in Randy's article. Is there a reason a tank will consume more alkalinity than Calcium? I have some montoporas and soft corals. I stopped adding Reef fusion 1/2 a month or so ago.

Randy Holmes-Farley · Jul 28, 2015

All tanks with hard corals or coralline algae will consume roughly 18-20 ppm calcium for each 1 meq/L (2.8 dKH) of alkalinity. You probably are too, but with kits barely able to distinguish 18 ppm calcium but 1 meq/L is a big percentage of the alk present. Also, many salt mixes start excessively high in calcium, so a decline from, say 480 to 460 ppm hardly seems significant, while 3 meq/L to 2 meq/L is big.

That said, one way to consume alkalinity is if nitrate is rising (not steady, but actually increasing) because the production of nitrate from ammonia uses alkalinity.

twilliard · Jul 28, 2015

That's why my ALK dropped after adding more fish.
learn something new every day!

Randy Holmes-Farley · Jul 28, 2015

twilliard said:
That's why my ALK dropped after adding more fish.
learn something new every day!

FWIW, I discuss such issues here:

When Do Calcium and Alkalinity Demand Not Exactly Balance? by Randy Holmes-Farley - Reefkeeping.com

dirtdobber06 · Jul 28, 2015

I suspect (along with others on this site) that I have a "nutrient problem. I posted some pics over in the member tank section because I have a lot of macro algae growing in my DT. I am trying to get rid of this as it is unsightly to me. That is why I started dosing Vinegar. I am building up to 60 mL/day and am at 20 mL/day and in the 3rd week of this. Should I keep adding bicarbonate? Should I keep dosing vinegar?

Randy Holmes-Farley · Jul 28, 2015

Adding vinegar to drive bacterial growth using existig nitrate and phosphate in the water will actually produce alkalinity, so there's no reason to stop the vinegar, and continuing to dose something to maintain alkalinity seems appropriate. Baking soda is a fine choice, as is limewater (kalkwasser) or a two part.