Dosing two part with drastically different dosing rates

[lilbitreefer]

I have a 120 mixed reef. Over the last month I have noticed I needed to keep upping my alk and lowering my ca dosing rates. Last rates were 9.2ml of alk and 1ml of ca. I run a co2 scrubber and maintain ph between 8.1-8.3 within a 24hr period. Magnesium was 1470 on feb 2.

I went from 7.78 to 7.5 alk in 10 days. When the alk was 7.78 I used the brs calculator to do a booster dose of 40mls alk but forgot to recheck alk the next day hence why I don’t have higher alk for initial reading but The booster was meant to bring the alk to 8.2. So theoretically it went from 8.2 to 7.5 in 10 days.

What I’m trying to figure out is why am I using up soo much alk but no ca? I don’t think I have much of a heavy load of corals. I originally was dosing equal parts but my ca kept skyrocketing so I tuned down the dose.

I am not terribly worried about it but I didn’t think it would be such a big difference. I just want to make sure I am going in the right direction make sure I’m not missing anything.
20% h20 change last week too.

My list of corals
2- 2x3” montipora brown with green polyps
1- 1.5” diameter montipora pink with maroon polyps
1 acan 1x2”
1x 1” leptastria
10 head frogspawn/hammer
1” maroon stag horn looking frag(unk spec.)
2”x2”x1” blue ridge
3small head acan blue/purple
5 small head tan acan
Recovering porites with about 10 tiny polyps I can count
Small colony of blasto
Some pictures of my colonies and the over all tank.

 

[Flippers4pups]

It's very possible that in dosing calcium and having it "skyrocket" as you say, it drove down your alkalinity through precipitation. Just a thought.

Here's a good read on this subject:


https://www.advancedaquarist.com/2002/11/chemistry

 

[lilbitreefer]

That’s a good article I read it a long time ago but good to read again. I find myself in zone 4 which basically just says to keep adding alk. I actually haven’t seen any signs of precipitate at all. The area where it is dosed has a pump to circulate the water and prevent a buildup so it actually goes into the tank.

 

[ckalupa]

Which two part are you dosing? BRS? Other two part systems are not necessarily dosed one for one to begin with (Red Sea)

A swing from 7.78 to 7.5 is not all that drastic though. Our test kits are not dead-on accurate. But if you see this trend then yes, adjustment is warranted.

 

[Randy Holmes-Farley Verified Community Expert]

It is not possible to have coral or precipitation demand that skewed (10:1), it is very close to 1:1 in all tanks, but water changes with mixes that do not match the tank, as well as certain other processes (rising or falling nitrate, sulfur denitrators, tap water top off, etc.) can impact the observed demand ratio, and when demand by corals or precipitation is very low (yours is very low) those other processes can become significant.

Day to day testing is too variable (inaccurate) to determine ratios. Look to longer trends.