Chemistry question

maksim serebro · Dec 20, 2015

Hi, Im trying to understand what is happening to my tank. Its a 300 gal mixed reef. I utilize BRS 2 part via a dosing pump. Accidentally left the calcium on last night and the calcium went up from 380 to 440. Alkalinity was 7.5. I checked the levels again this morning (10 hrs later). Calcium went down to 400 (which makes sense) but Alkalinity went UP to 8.7 My question is why would an increase in calcium cause an increase in alkalinity? What am I missing? Thanks in advance for helping!

maksim serebro · Dec 20, 2015

I was under the assumption that increased calcium would cause some precipitation and lower alkalinity. Why would alkalinity go up by itself?

Randy Holmes-Farley · Dec 20, 2015

You are not missing anything. Either what you added isn't exactly what you thought, or there's some testing error (which is very common).

Maybe the calcium just wasn't mixed in before the 440 result, but I very strongly doubt it declined that much overnight. If it did, alk would necessarily drop by about 5.5 dKH.

In any case, the values are fine right now, so don't worry too much.

maksim serebro · Dec 20, 2015

Thanks for the response! I left calcium dripping at 1.1ml per minute for over 2 hrs. I measured calcium levels as soon as I realized i left the doser on. It is completely possible that the 440 reading was erroneous since calcium did not mix in well. But that still does not explain the sudden INCREASE in alkalinity. I understand that a drop is possible, but an increase is strange.

Randy Holmes-Farley · Dec 20, 2015

The increase either is alk testing error, or you added some alk somehow and didn't realize it.

You are correct that there is no possible way for it to rise if all you added was calcium chloride.

maksim serebro · Dec 20, 2015

BTW, i am using red sea testing kits.

maksim serebro · Dec 20, 2015

Thanks Mr Holmes. I also read in one of your articles that you should not increase only one variable at a time. Both alkalinity and calcium should be adjusted at same time. Did I understand it right?

Randy Holmes-Farley · Dec 20, 2015

maksim serebro said:
Thanks Mr Holmes. I also read in one of your articles that you should not increase only one variable at a time. Both alkalinity and calcium should be adjusted at same time. Did I understand it right?

Well, perhaps not. If one one needs adjusting, you should adjust only that one.

twilliard · Dec 20, 2015

When not dosed equal I call it a correction dose.

maksim serebro · Dec 20, 2015

got it! Thanks!

Randy Holmes-Farley · Dec 20, 2015

Right. For routine dosing, dose both equally. If one needs a big boost (especially calcium), add just it, as you did.

maksim serebro · Dec 21, 2015

I think I may have solved the mystery of increasing alkalinity. Both calcium and soda ash were administered via dosing pumps. When the calcium pump was left on, the corals got stressed and stopped growing and absorbing bicarbonate, so it kept rising because of the pumps. I turned off all dosing pumps and the measurements (both for calcium and alkalinity) have not changed in two days. I hope the corals can recover. No visible damage is noted as of yet.

Randy Holmes-Farley · Dec 21, 2015

maksim serebro said:
I think I may have solved the mystery of increasing alkalinity. Both calcium and soda ash were administered via dosing pumps. When the calcium pump was left on, the corals got stressed and stopped growing and absorbing bicarbonate, so it kept rising because of the pumps. I turned off all dosing pumps and the measurements (both for calcium and alkalinity) have not changed in two days. I hope the corals can recover. No visible damage is noted as of yet.

FWIW, I don't think elevated calcium (less than 600 ppm, anyway) stresses corals.

twilliard · Dec 21, 2015

Randy Holmes-Farley said:
FWIW, I don't think elevated calcium (less than 600 ppm, anyway) stresses corals.

Correct me if wrong Randy, thanks!
Elevated calcium is typically met with a higher chance of precipitation.

Randy Holmes-Farley · Dec 21, 2015

twilliard said:
Correct me if wrong Randy, thanks!
Elevated calcium is typically met with a higher chance of precipitation.

Yes. Higher calcium, alkalinity and pH all contribute to more rapid precipitation of calcium carbonate.

maksim serebro · Dec 21, 2015

I did not see any precipitate. I used to dose 57 ml of soda ash per day to maintain alkalinity of 7.5 For the last two days I have not dosed any and my alkalinity went up and stayed at 8.4 I am at a loss then. Calcium is 420. Nothing else has changed.

twilliard · Dec 21, 2015

Is there such a thing as overdosing to a point of saturation where test kits will not show an increase of elements?
You see threads like "I cant increase my ALK no matter what I do"

Breadman03 · Dec 21, 2015

twilliard said:
Is there such a thing as overdosing to a point of saturation where test kits will not show an increase of elements?
You see threads like "I cant increase my ALK no matter what I do"

I think it's likely, but diluting the sample would allow one to extend that range.

Randy Holmes-Farley · Dec 21, 2015

twilliard said:
Is there such a thing as overdosing to a point of saturation where test kits will not show an increase of elements?
You see threads like "I cant increase my ALK no matter what I do"

No. Our alk and calcium kits can detect any amount likely to be there. It will just take more and more titrant as the values get higher and higher.

People who say that are not trying hard enough.