Rising Alk with Falling Ca.... Why??

[JaredB]

Good afternoon and thank you in advance for helping me. I have a relatively new tank (been up for about 8 mos), fairly well stocked mixed reef. Red Sea reefer 525 XL. Until recently i have not had to dose. Continuous water changes were maintaining my ca/alk/mg levels pretty well. When I started dosing it was with kalkwasser through an avast marine kalk reactor fed by one head of a Neptune DOS pump with water from my freshwater top off reservoir. The effect on my tank pH was favorable and maintaining my levels was pretty effortless.
Within the past month demand has exceeded what I want to dose in kalk water (which is about 750ml/day) so I started dosing. Because i still had one dosing head left on my DOS pump, single solution dosing appealed to me and I decided to go with carbocalcium (calcium formate).
I’ve reached a situation where my alk remains stable (around 9 dkh), but my ca continues to decline daily. I manually dose to reset my desired ca level (around 450), but the levels decline despite stable alk.
I didn’t think this was supposed to happen with balanced dosing additives.
I am currently carbon dosing with NO3PO4x for nutrient control. My nitrates are stable around 2ppm. My phosphates are a little higher than I would like (around 0.1).
I do not have clams.
general parameters:
Temp 78
Salinity 1.026
PH 8.1-8.3
Ca 420-450
Alk 9
Mg 1400
No3 2
Po4 0.1

i do not see any obvious precipitation in the tank.
Thank you again for your opinion and advice.
jared

 

[Randy Holmes-Farley]

Precipitation cannot ever be an explanation of something like this.

maybe you are not dosing the volumes you think, are dosing an additive not made for 1:1 dosing, water changes are messing with ratios, or the product wasn’t made or diluted exactly right.

declining nitrate and nitrate dosing also adds alk. So can tap water for top off.

 

[JaredB]

Rodi water exclusively.
not dosing nitrates and nitrates pretty stable Just no3po4x dosed
Carbocalcium measured out with digital scale to .01g accuracy. And can’t mess up kalk.
I do have a big sponge infiltration on my rocks and in sump??
Water changes is interesting. Could changing out 2gal a day cause a decline in ca. I’m using tropic marine pro reef

 

[JaredB]

Precipitation cannot ever be an explanation of something like this.

maybe you are not dosing the volumes you think, are dosing an additive not made for 1:1 dosing, water changes are messing with ratios, or the product wasn’t made or diluted exactly right.

declining nitrate and nitrate dosing also adds alk. So can tap water for top off.

I looked up the parameters of the mixed salt. Alk mixes to 7 and calcium to 440. If continuous water changes were having an influence then Alk should trend down and ca should remain fairly stable. I’m seeing the opposite effect.
Any other thoughts? What else would consume calcium without alkalinity?
Thank you!

 

[Randy Holmes-Farley]

Any other thoughts? What else would consume calcium without alkalinity?
Thank you!

There is nothing that reduces calcium and not alk except water changes. A source of alk is still a possibility, as is testing error.

 

[JaredB]

There is nothing that reduces calcium and not alk except water changes. A source of alk is still a possibility, as is testing error.

I’m using a Neptune trident for all testing. Suppose i could do a calibration.
What else could introduce Alk and not ca? The water that I use for water changes has an Alk around 7 and I’m targeting 9 for the tank. Shouldn’t be a source of increasing Alk. What else could add Alk?
Thank you Randy. I’m so frustrated by this. Goes against everything I’ve read

 

[Randy Holmes-Farley]

This article describes all of the real and perceived reasons for alk and calcium demand to not match that I am aware of.

http://reefkeeping.com/issues/2004-12/rhf/index.htm