Why would my Alk stop falling?

[Timrpn]

i have been testing my water almost everyday for the past 3 weeks to determine what my Alk usage is. It was consistently falling by .2 Dkh daily. All of a sudden it has maintained 9.4 for 4 days on a row now. I have even added more sps frags to the tank over the past couple weeks. What would make it stop depleating? I am trying to get it down to 8 dkh. I have not done any water changes or dosed anything. Just top up with RODI ATK.

I am using Hanna Alk test kit.

 

[Cory]

Whats your no3 and po4?

 

[ihavecrabs]

A lot of things can cause alkalinity to stop decreasing. Most notably corals using less which can be caused by almost anything (including looking at them the wrong way, haha).. Mostly lighting changes, handling/moving, flow changes, nutrient changes, temp, etc

If you have a new tank, sometimes it takes a while to balance.. I've suspected mined dry rock or dry rock in general to uptake alk to come to equilibrium, but this is just speculation through experience. So if you added new rock and it came to equilibrium, it may show as consuming less..

Has your pH or temperature changed drastically? Were you taking readings at the same time of day?

 

[TessGlo]

Whats your no3 and po4?

I've noticed several times in my tank that if my nutrients get to low, alk consumption slows. Good thing is you are testing so can stay on top of it.

 

[AdamNC]

I've noticed several times in my tank that if my nutrients get to low, alk consumption slows. Good thing is you are testing so can stay on top of it.

I’ve noticed just the opposite. But I also run a ulns SPS tank.

 

[Randy Holmes-Farley Verified Community Expert]

It may be a real variation, or a random variation of the tester. 0.2 dKH is well under the claimed uncertainty of the checker.

0.2 dKH is a very low value, and small real changes in the tank could cause it, especially pH differences.