Magnesium effect on alkalinity

WillB · Aug 10, 2018

Hey guys. I have a 29g mixed reef tank that is beginning to frustrate me. My problem is that over the last week, my alkalinity has dropped from 8.0 to 7.3 and my magnesium has dropped from 1380 to 1320. My calcium has stayed rock solid at 450 every test. I am surprised to see the magnesium drop because I increased my dosage last week by 1mL as it dropped slightly from past tests.

So I’m wondering... could my dropping magnesium be the cause of my dropping alkalinity? Why isn’t calcium dropping at the same rate? I dose b-ionic 2 part and their magnesium as well.

Another external factor that I have considered is that we are having a heat wave here in San Diego. Temperature wasn’t even registering on my stick on temperature sensor yesterday (maxes out at 86). Today I have ac running and fans blowing so that should get better.

I don’t know. What do you think?

Diesel · Aug 10, 2018

I’m afraid if that stick-on

reads 86 that would be your problem of your parameters are off.
Then again those stick-on’s are far from reliable.

WillB · Aug 10, 2018

There is no doubt in my mind that it is right haha

WillB · Aug 10, 2018

Diesel said:
I’m afraid if that stick-on reads 86 that would be your problem of your parameters are off.
Then again those stick-on’s are far from reliable.

Like a pig in the desert... I’m bacon out here!

WillB · Aug 10, 2018

So should I not adjust my parameters? Just get temp under control and hope for the best?

Diesel · Aug 10, 2018

Bingo!

WillB · Aug 10, 2018

Workin on it!

WillB · Aug 10, 2018

Thanks!

WillB · Aug 10, 2018

Thanks!

Randy Holmes-Farley · Aug 11, 2018

WillB said:
Hey guys. I have a 29g mixed reef tank that is beginning to frustrate me. My problem is that over the last week, my alkalinity has dropped from 8.0 to 7.3 and my magnesium has dropped from 1380 to 1320. My calcium has stayed rock solid at 450 every test. I am surprised to see the magnesium drop because I increased my dosage last week by 1mL as it dropped slightly from past tests.

So I’m wondering... could my dropping magnesium be the cause of my dropping alkalinity? Why isn’t calcium dropping at the same rate? I dose b-ionic 2 part and their magnesium as well.

Another external factor that I have considered is that we are having a heat wave here in San Diego. Temperature wasn’t even registering on my stick on temperature sensor yesterday (maxes out at 86). Today I have ac running and fans blowing so that should get better.

I don’t know. What do you think?

That magnesium drop is either test error ( most likely), a salinity change, or a water change with a low magnesium mix. Magnesium can NEVER drop that much in a week by consumption or precipitation unless you massively overdose alkalinity.

Randy Holmes-Farley · Aug 11, 2018

WillB said:
So should I not adjust my parameters? Just get temp under control and hope for the best?

The magnesium is not dropping due to elevated temps.

WillB · Aug 11, 2018

Randy Holmes-Farley said:
The magnesium is not dropping due to elevated temps.

Thanks Randy. I’ll redo both tests when I get home. Does temperature have an effect on alkalinity?

WillB · Aug 11, 2018

I didn’t do a water change that week or allow salinity to change from 1.025 so it must be test error

Diesel · Aug 11, 2018

WillB said:
Thanks Randy. I’ll redo both tests when I get home. Does temperature have an effect on alkalinity?

It does in a way.
Randy discusses that in this link under temperature http://reefkeeping.com/issues/2004-05/rhf/

WillB · Aug 11, 2018

Diesel said:
It does in a way.
Randy discusses that in this link under temperature http://reefkeeping.com/issues/2004-05/rhf/

Increases the metabolism so increased alkalinity consumption. That makes sense. I would expect that the increased alk consumption would be proportional to calc consumption but I guess not this time! I’ll retest and if comes out the same, bump up my alk dose a little