Alk and Ca trend doesn’t make sense.

[GillMeister]

I'm dosing ATI Essentials at 1:1 but my calcium is dropping while alkalinity is climbing. I started at 450 ca 2 weeks ago and alk was 8.4. Now my values are Ca 380 and alk is 11.2.

I've taken three tests in the last three weeks and these latest results are not outliers. They follow the expected trend line.

Has anyone had similar issues with a 2 part system?

 

[Randy Holmes-Farley Verified Community Expert]

Assuming ATI made it correctly (not all companies do make 1:1 correctly), there are still reasons why there is an imbalance.

Test error is a big reason folks "observe" imbalances.

One real reason is rising or falling nitrate, which consumes or adds alkalinity. In your case, falling nitrate could explain it.

Other additives may add alk without your knowing it.

Top off tap water can mess with ratios.

Another big one is that folks sometimes assume incorrectly that 2 dosing pumps are dosing the same rate.

 

[nereefpat]

That's a great list, Randy.

 

[GillMeister]

Nice summary.

Assuming ATI made it correctly (not all companies do make 1:1 correctly), there are still reasons why there is an imbalance.

Test error is a big reason folks "observe" imbalances.

One real reason is rising or falling nitrate, which consumes or adds alkalinity. In your case, falling nitrate could explain it.

Other additives may add alk without your knowing it.

Top off tap water can mess with ratios.

Another big one is that folks sometimes assume incorrectly that 2 dosing pumps are dosing the same rate.

I think my test results are accurate. Very solid trend line and I'm very careful when testing. My DOS pumps are dosing almost perfectly 1:1. The DDR levels are dead even. And I use RODI for top off water.

The nitrate comment is probably 100% the cause. I didn't realize there's an affect with that. I had been dosing nitrate but cut way back due to an outbreak of ulva. I cut back, wait for it, 2 weeks ago.

 

[Randy Holmes-Farley Verified Community Expert]

Nice summary.
I think my test results are accurate. Very solid trend line and I'm very careful when testing. My DOS pumps are dosing almost perfectly 1:1. The DDR levels are dead even. And I use RODI for top off water.

The nitrate comment is probably 100% the cause. I didn't realize there's an affect with that. I had been dosing nitrate but cut way back due to an outbreak of ulva. I cut back, wait for it, 2 weeks ago.

OK, yes, dosing nitrate adds alkalinity.

 

[GillMeister]

I'm back to being confused. I stopped dosing nitrates 2 weeks ago and my alk started increasing.

Time for some small water changes.

 

[blasterman]

Confused.

Alk is increasing in a static tank, or the ratio of alk to calcium you are dosing is showing a slowing of alk consumption?

 

[GillMeister]

Confused.

Alk is increasing in a static tank, or the ratio of alk to calcium you are dosing is showing a slowing of alk consumption?

I'm dosing ATI Essentials 2 part solution at a 1:1 ratio. My tank is consuming Ca much faster than alk causing them to be out of balance. In 2 weeks my Ca has decreased and my alk has increased in the tank.

 

[Randy Holmes-Farley Verified Community Expert]

I'm dosing ATI Essentials 2 part solution at a 1:1 ratio. My tank is consuming Ca much faster than alk causing them to be out of balance. In 2 weeks my Ca has decreased and my alk has increased in the tank.

Simple answer is reduce the alk dose and increase the calcium dose. Lots of things can explain this result: inaccurate testing, inaccurate solution concentrations, inaccurate dosing amounts, alk being added other ways, etc.