Dropping Alkalinity in a new tank

MTShell

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Hello guys,

As my title says, I have a decreasing alkalinity in a new tank. I understand the logic of consumption of alk by corals, some more some less, but I am not aware of the processes and reasons of alk consumption in a tank that does not have corals yet.

Timeline: on august 3rd I started my 220 gallon cycle, with dead cured rock and live sand. by august 31st my cycle finished and I could get rid of ammonia under 24 hours.
At that point, my very first alk measurement said 8.6. As my diatoms started appearing and overtaking the tank, I have been progressively adding snails and blue legs to manage. By now, the diatoms are dealt with through time and snails. DKH readings went like this: September 5th 7.8, september 24th 6.7, october 4th 6.0. I have only done 40% water change at cycle completion to lower nitrates, and did not test very often. My logic was that the tank is relatively bare and my nitrates were only slowly dropping, so no need for water changes. I did not expect my dkh to drop that much and I do not know the reason for the drop.

I have a GSP frag since september 30th and a zoa plug since ocotber 2nd, so it could not have been those.

Now, I am planning on getting alk back to 8.0 dkh using sodium bicarbonate and then measure my consumption daily, + start 2 part accordingly.

Is that a logical plan? Should I instead be doing many water changes? I am kind of against that because my tank is nutrient deprived at this point anyway, so much so that I want to restart ghost feeding while my first 10 fish are completing QT. I plan to do weekly 10% water changes once my fish are in.

Thanks for any suggestions and feedback:)
 
Things that reduce alk in new tanks are precipitation of calcium carbonate and accumulation of nitrate.
 

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