large drop in alk

[asome_one]

So I'll try my best to keep this short...ish

Today I noticed my hammer (11 days in the tank) looked terrible. It is retracted and has a lot of its skeleton showing. This prompted testing values. I don't have an MG test.
15G tank
IO Reef crystals
salinity 1.026
nitrate 1.5
phosphate .06 (hanna)
alk 9.3
calcium 450

I have had the rock for the tank running for about 2 years. I swapped from a fluval flex 15 to a IM 15 about 2 months ago and moved everything over.
I tested phos and nitrate religiously for the past 3 months prior and after moving. I dose neophos daily to maintain .03-.06 phos.

My alk has been consistently around 12.0 on 2/05 it was 12.5 on 3/05 it was 12.5. I figured 2 months stable, good to go, don't need to check. Today its 9.3. Now this would make me think my corals are just eating it up. I went to a reef expo on 4/1 and obtained my first set of lps. Favia, leptastrea, acans, and a hammer. Prior to this I only kept anemones, zoas, toadstool, and shrooms. However!! I checked my source mixed saltwater, that I have not remixed or touched for at least 2 weeks. It is also
9.3alk and 1.026. My mixed saltwater was on par with the tank before. around 12.0-12.5.
So the drop is in both the tank and the mixed water.

I have an ato that tops off with RODI. My TDS is zero for the ATO water.

Prior to adding any LPS, about 3 months ago, I did add 1 dose of 5ml All for Reef which skyrocketed my alk to 13+ so I just never added it again.
Everything else in the tank looks fine. All have good extension and nothing else looks unhappy. I moved the hammer to a lower flow area.

I am unsure when my alk dropped from 12. I will obviously be rechecking daily now to see if it goes lower. However, it doesn't solve why the premixed saltwater is low without intervention and the tank is matching. It has gotten considerably warmer recently? The tank hasn't gone over 79 degrees but with the windows being open its possible more water is being topped off daily. It still doesn't make sense why the premixed alk is so similar. Maybe I'm just drawing similarities somewhere I shouldn't be.
Any help would be greatly appreciated.

 

[Randy Holmes-Farley]

Raw salt water with high alk often precipitates calcium carbonate in the reservoir, reducing alk.

There are a variety of processes that consume ilk in a tnak,such as precipitation of calcium carbonate, increasing nitrate, and consumption by a wide range of organisms (not just corals and coralline algae).


I wouldn't agonize over what caused it unless there is a problem.

 

[asome_one]

I'll chalk my hammer dying up to being a casualty of something other than my alk then.
Thank you!