Calcium moving out of sync with Alkalinity

[milonedp]

I've recently set up an Apex Trident and finally have my Alkalinity rock solid, testing at 12 times per day it ranges from 8.01 to 8.09 over a 24 hour period with each hour roughly what the same hour was the prior day

Calcium however is dropping from 435 to 420 in one 24 hour period then 420 to 390 in the next 24 hour period.

I'm using BRS 2 part dosed at 140ml per day, 430 gallon mixed reef with a decent amount of LPS and SPS.

Why would calcium be dropping if I'm adding in proportion.

Mg is stable at 1340 to 1360 and I rarely need to add any.

I've seen calcium stable with alk moving but not the other way around. Could the 140ml be too much and it's causing precipitation of calcium?

Any thoughts?

 

[Randy Holmes-Farley Verified Community Expert]

I’m not sure if you made and dosed solutions correctly, or if salinity is changing, but there is no possible way for calcium to decline without alkalinity declining, except, of course, if you are adding alkalinity somehow.

I’d keep watching calcium as it may just be test error. Actual consumption of 30 ppm calcium must be accompanied by consumption of about 4 dKH of alkalinity. There is no other sink for calcium.

 

[milonedp]

I’m not sure if you made and dosed solutions correctly, or if salinity is changing, but there is no possible way for calcium to decline without alkalinity declining, except, of course, if you are adding alkalinity somehow.

I’d keep watching calcium as it may just be test error. Actual consumption of 30 ppm calcium must be accompanied by consumption of about 4 dKH of alkalinity. There is no other sink for calcium.

Okay thanks, I knew something wasn't making sense. Just to make sure I understand, even if the alk was being dosed too high it shouldn't cause calcium to precipitate which could lower the calcium right?

I do a 3-gallon automatic water change with Tropic Marin Pro Reef at 1.026. Now that you mentioned salinity (which is stable overall) but it made me wonder if a test was triggered near when a freshwater top off occurred that should affect alkalinity and ca in the same proportion right, i.e. that shouldn't be causing this either?

If that's true then I suspect you are right, I must have made one of the solutions too strong or too weak. Assuming that is the case, is it okay to have them dose differently i.e. 140 alk and 160 ca until the batch is used up? Or is there a way to test the solutions themselves so I can correct them?

 

[Randy Holmes-Farley Verified Community Expert]

Okay thanks, I knew something wasn't making sense. Just to make sure I understand, even if the alk was being dosed too high it shouldn't cause calcium to precipitate which could lower the calcium right?

If that's true then I suspect you are right, I must have made one of the solutions too strong or too weak. Assuming that is the case, is it okay to have them dose differently i.e. 140 alk and 160 ca until the batch is used up? Or is there a way to test the solutions themselves so I can correct them?

It’s fine to dose them slightly differently, especially if it is based in long term testing over weeks, not daily tweaks based on calcium changes with are probably mostly test error.

Some other factors, such as water changes, can mess with the relative need for the two solutions.

 

[milonedp]

Thanks so much, I appreciate the responses and all you do for the hobby

 

[Randy Holmes-Farley Verified Community Expert]

You're welcome and thanks!

Happy Reefing.

 

[milonedp]

I went to do a bolus dose and turns out the DOS lost suction on the Ca because of the murloc bulkhead and hard tubing I was using, so no Ca was being dosed...

 

[Randy Holmes-Farley Verified Community Expert]

That makes sense. Thanks for the update.