Alkalinity dropping all the time, yet calcium etc. holding

[pmaddox]

For some time now i've experienced a constant drop of my Alkalinity although my Calcium and Magnesium do not drop remotely as fast.

It's perplexing.

Does anyone have experience or insight as to what could be causing this?

 

[morpheas]

What kind of drop are we talking about? It's normal for alkalinity to move much faster than calcium (and definitely magnesium). Do you have any numbers to share? Also what volume system? SPS, LPS, softies?

@Randy Holmes-Farley has excellent articles in the interwebs like this one.

 

[Randy Holmes-Farley]

Unless you monitor for an extended period, a hobby calcium kit may not accurately detect the small calcium drop (13 ppm) that is associated with an easily detected 2 dKH drop in alkalinity.

Otherwise, there are a few ways alkalinity can decline and not see a calcium drop, such as increasing nitrate (not just high, but actually rising) or the use of a sulfur denitrator.

 

[pmaddox]

Thanks guys these points are helpful. If you view the 150g tab in this spreadsheet you can see my tank history for more clarity.

https://docs.google.com/spreadsheets/d/17hGDk1hSgmBUhVNmyJh7MQ0C8uAdMzveuJd6iMef8uQ

Also, the tank is about 70/30 soft to hard corals.

 

[Randy Holmes-Farley]

What are you dosing?
What salt mix are you using for water changes?

 

[pmaddox]

I have been dosing Seachem reef builder Alkalinity and I use Reef Crystals (Instant Ocean) salt. It looks like I drop about .20 dKH per day. 200 gallons of water (not counting any displacement)

 

[Randy Holmes-Farley]

0.2 dKH per day?

You'd wait a long time to detect a calcium drop. It would only be about 1.3 ppm per day, so it might take a few weeks to reproducibly see a calcium decline using a hobby kit.