Phosphates and Alkalinity Consumption

Todd31 · May 2, 2018

Hello...

While i understand that increased phosphates inhibits calcification... I did not realize how drastic of a difference it can make.

my typical parameters

nitrate 5 to 7
phos .05 to .08
Alk 7.8

I recently started feeding the tank more... Specifically corals in effort to increase coloration and health. This caused a bump in phosphates up to .15 .... which then caused alk to spike up to 8.4 because i had not adjusted my 2 part dosing yet ... So, i changed out my reactor with fresh carbon/GFO... which the next day brought phosphate down to .10 ... i then tested alk and got 7.6 ...

Not good having all this bouncing around... hopefully i didnt hurt my sps.

I guess the moral of the story is that until i find the sweet spot its pretty important to test that ALK every day.

Is it typical to have a phosphate spike cause that much change in consumption? This is a 75 gallon mixed reef with a decent amount of SPS.

cheers!

Brew12 · May 2, 2018

I was under the impression that PO4 wouldn't start inhibiting calcification until it was over 0.2ppm and possibly significantly higher.

If I had to guess, it is the changes causing the decrease in alk consumption more so than the PO4 inhibiting calcification. I'm going to need to look into this more.

Randy Holmes-Farley · May 2, 2018

Phosphate will also reduce abiotic precipitation. it isn't just impacting corals (maybe not even mostly).

https://link.springer.com/article/10.1007/BF00006476

"Laboratory work has shown that phosphate is adsorbed onto calcite and aragonite surfaces and inhibits crystal growth rates"