Large dKH drop after dosing Sodium Carbonate

[marxman]

Hi All,

I had a question about dKH levels after dosing. I have recently been trying to raise / alter my Alkalinity level of my tank as I was running low, sometimes dipping below 7.

I began adjusting my daily dosing of AquaForest KH Plus (I'm moving away from this as it's too expensive for my larger tank).
I also began using 1 time daily dosing of BRS Soda Ash to get the Alk reading to where I wanted it.
I have a Trident so it takes readings every 6 hours for my absolute amusement

My question is this...
What is the reason for when I dose Soda Ash, the Alk raises 1.0dKH to where I want it, and then within the next 6 hours there is a about 0.3dKH drop. Then the subsequent readings seem to level off... as my dosing accommodates for the tank usage.
What is the cause for this initial drop? Is this a Carbonate vs. BiCarbonate thing?
Would I see a different trend if I did a 1 time dosing of BRS Sodium BiCarbonate for the 1dKH elevation?

Thanks in advance

 

[Randy Holmes-Farley Verified Community Expert]

There is not reason for a drop aside from possible consumption, very slow dilution into remote parts of a complex system (sumps/refugia, etc) abiotic precipitation, or test error.

 

[Randy Holmes-Farley Verified Community Expert]

Bicarbonate may give less precipitation, and may lower pH a bit lowering demand by organisms. Nothing wrong with using it.