no clue whats going on or if this is normal

[20 gallon]

Calcium: 520
Alk: 7
pH: 8.0

About 5 days ago alk was 9 and ph was 8.1
is it normal for alk to drop so much with calcium remaining so high?
keep in mind i have about 20 gallons of water volume, and about 8 sps/lps coral frags

[nereefpat]

A drop of 2 in five days is perfectly reasonable. Corals and coralline algae is probably what is using it. Looks like you may have to start dosing for alk in some way (baking soda is a good way)

[blanden.adam]

Agreed. That's a completely normal drop.

Calcifying organisms consume ~7 ppm of calcium for every 1 dKH of alk. So with a drop of 2 dKH, you'd only expect a 14 ppm drop in calcium, which is within error of our tests. So, when deciding how much of a balanced additive to dose, we always follow the alk -- it's way more sensitive.

This website should help you make your dosing calculations: http://reef.diesyst.com/chemcalc/chem_calc3.html

Good luck!

[20 gallon]

Awesome, thanks, I'm dosing baking soda as we speak.