Is there a chemical process where Calcium in the reef tank can increase on its own?

[jkobel]

My question - is there a process in the tank that would allow the Ca in the water to increase over time without the addition of a supplement like 2 part?

I have been seeing an issue with the test results from my Trident over the last couple weeks where the readings do not seem to match my expectations based on dosing and assumed consumption.

On 2/10, I made a corrective does of 2 part and waited 1 day, at which time I tested my water with my Hanna getting a Calcium reading of 414 while the Trident reading was 422, these two readings were very close and I felt fine about that.

I also had turned off my 2 part dosers because i wanted to measure my consumption over a 3 day period.

The attached graph is my readings from this morning, the Ca is increasing after the initial drop after the corrective dose. The first 2 readings after the reading i checked against the hanna are within the stated level of precision of +/-15ppm (although the upward trend is concerning) but the reading form midnight is outside of that range. I'm waiting for noon so i can take a sample of tank water and test again with hanna so that there is no variation from the sample since that wen the next scheduled Trident test is.

Tank params
ph 7.9
temp 78.3
Ca 457
Alk 8.55
Mg 1330
TWV - ~140gals

tank is mixed reef and stable running 3 years.

I'm having a hard time envisioning the issues here, wondering if there are others factors so any help is appreciated.

 

[Randy Holmes-Farley]

A 30 ppm rise over 3 days of no calcium dosing is almost certainly test error unless the salintiy is increasing substantially in that same time.

 

[jkobel]

Water volume is stable

 

[jkobel]

What is a reasonable consumption rate of Ca for a 140gal light to moderately stocked mixed reef tank?

I understand that question might be vague but this whole thing started by me thinking that the math doesn't add up RE: my actual dosing vs the trident readings vs what I would need to dose to account for the 16-21ppm dips and spikes I regularly see on the trident.

Having to dose 760ml of Ca to get from 387->440 is a far cry from the 30ml i dose daily.

What am I missing? this Graph shows my Alk and while I dont understand the regular bumps since the corrective does (I am not dosing anything currently) the trend seems logical to me. Although the Hanna and Trident are off by 1.25 dkh (Trident reading lower) at least the trend seems ok.

Maybe this isnt a chemistry question either, I'm not really sure what help I need, i just know this isnt adding up

 

[Randy Holmes-Farley]

What is a reasonable consumption rate of Ca for a 140gal light to moderately stocked mixed reef tank?

I understand that question might be vague but this whole thing started by me thinking that the math doesn't add up RE: my actual dosing vs the trident readings vs what I would need to dose to account for the 16-21ppm dips and spikes I regularly see on the trident.

Having to dose 760ml of Ca to get from 387->440 is a far cry from the 30ml i dose daily.

What am I missing? this Graph shows my Alk and while I dont understand the regular bumps since the corrective does (I am not dosing anything currently) the trend seems logical to me. Although the Hanna and Trident are off by 1.25 dkh (Trident reading lower) at least the trend seems ok.

Maybe this isnt a chemistry question either, I'm not really sure what help I need, i just know this isnt adding up

The actual consumption won't be more than about 20 ppm of calcium for each 2.8 dKH of alk consumed. There's no mechanism for significant calcium consumption side from calcium carbonate formation.

In a day, alk might typically be consumed 0-3 dKh per day, maybe higher in very heavy SPS tanks. Thus, calcium consumption ranges from 0 to about 25 ppm calcium per day.

 

[Randy Holmes-Farley]

Many people have issues with Trident accuracy, especially when reagents are getting low.

However, while I'm not sure what you are dosing, a typical two part (e.g., by DIY recipe #1) will take 760 mL to raise 140 gallons by 53 ppm.

 

[jkobel]

So, I think I have been over dosing my Calcium. I have been adding about 28 ml /day but it seems I might only be consuming about .48 dkh/day of Alk. I haven't noticed any precipitation, is there a downside to over dosing Ca? (besides wasting $$)

 

[Randy Holmes-Farley]

So, I think I have been over dosing my Calcium. I have been adding about 28 ml /day but it seems I might only be consuming about .48 dkh/day of Alk. I haven't noticed any precipitation, is there a downside to over dosing Ca? (besides wasting $$)

Rising calcium is the only issue, and it is fine up to at least 550 ppm.

 

[jkobel]

Thanks Randy

 

[Randy Holmes-Farley]

You're welcome.

Happy Reefing.