Factors influencing Alk depletion rates?

[Delphinus]

What are things to look for if you find that Alk suddenly stops depleting at the rate it was going at for a while?

In the last two weeks my Alk stopped depleting. I would dial back the doser but I ended up taking it all the way offline about 5 days ago and even with no dosing the Alk is only dropping about 5ppm per day (it got as high as 200ppm or 11dKH, whereas normally I target it around 140ppm, or about 8.0dKH).

Calcium is still being dosed and sits around 370.

Magnesium sits around 1450 currently.

I didn't think to test tank pH last night but it occurs to me now maybe I should. Seems to me something is up. I'm not sure what to look for here. Any thoughts?

FWIW nitrate is unreadable on the test kits I have, and phosphate tests out around 15-30 ppb on the Hanna handheld (so around 0.015 - 0.03 ppm). I don't know if that's a high value or not. Honestly I would have expected it to be zero as I run zeovit but I'm starting to understand that I actually understand next to nothing, these days

[reefwars]

Originally Posted by Delphinus

I didn't think to test tank pH last night but it occurs to me now maybe I should. Seems to me something is up. I'm not sure what to look for here. Any thoughts?

ph could be something to conside...are you running a hrv in yor house?? if not could be the sudden change in weather we just got and not as much fresh air entering the house.

other than that i have no idea unless something changed in the way of salt batch or something?? idk

[reefwars]

any difference in your corals you notice??

[lastlight]

You're confident you weren't dosing more than you thought?

[Money pit]

According to RHF in this article
http://reefkeeping.com/issues/2004-05/rhf/index.php
Your Po4 is fine.

[TimT]

Alkalinity depletion is a sign of growth so I think it safe to assume that the growth has stopped or been greatly reduced. Some thing has either disrupted it or a nutrient is so low that it is limiting it.

I have found that temperature fluctuations(~3+°f) will cause a disruption.

pH out of range of 7.8-8.4 can have an effect.

Have you tested your water for copper? As RO membranes age they begin to pass more copper. Some houses still have copper pipes.

What is your salinity and has it changed recently?

Your Ca seems a bit low. I would recommend at least 400ppm.

When was the last water change? Was the salt mixed to redistribute the chemicals before being added to the water? Have you switched salt brands recently?

SPS do rely on zoozanthellae for energy and the zoozanthellae rely on nitrate for food. Having 0 nitrate could be a limiting factor.

Just some ideas.

Cheers,
Tim