If I were to take a guess, the reason why your dKh is dropping when you add Ca is because your inhabitants are finally getting the Ca they need to consume the carbonates. With Ca that low, I pretty much guarantee it is not precipitating out with the dKh, so that suggests your dKh is being consumed along with the Ca as soon as you are adding the Ca. I would increase your Ca and dKh dose until you see your Ca increasing and your dKh steady. Dose one when you wake up, the other when you go to bed. You may be surprised how much of these your tank goes through when it has good levels. I started dosing at 20ml dKh and had it up to 200ml/day before I could get it to stay level above 8.
Dan
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