I might be over-thinking again... in my 2nd tank I'm dosing Balling classic. Calibration issues with the doser aside (Ca crept up to 5% overdosing relative to other channels), I think my KH consumption is faster than balance. I know this is not an unusual scenario for classic/Triton in itself. I'm wondering if this is not a case of the corals taking significantly unbalanced consumption, but could macroalgae be the culprit here? My reasoning is based on recently reading up on carbon intake by freshwater aquatic plants. They prefer CO2 as their primary carbon source, but some plants have adapted to also take bicarbonate in some form to supplement it. In seawater, we have a pretty much guaranteed supply of bicarbonate so it would seem logical if marine plants have evolved to make use of such alongside available CO2. I've been having minor algae problems in the DT, and to try and fix that, I significantly increased the sump light cycle to 22h on, 2h off. This is working and most of the unwanted algae has died off in the DT. I didn't make note of when I did this, but I think it roughly coincides with a drop in measured KH starting around a month ago. The off period was introduced since I read that having a light cycle produced more growth than continuous lighting. I haven't seen any research into at what might be the optimal photoperiod. Where is the point where more light duration becomes counter-productive? Anyway, the sump contains mainly chaeto, but recently I also introduced some caulerpa racemosa. Also I've inadvertently created an algae scrubber which decided to form on one of the sump partitions. Anyway, given the growth of the sump algaes, I have to wonder if they might be enough to take a significant amount of bicarbonates out of the system. If no one has done so before, I'm debating doing a test myself. The next time I harvest chaeto, I could place it in a spare small tank next to a south facing window. I could dose the water with fertiliser so growth isn't limited by nutrient availability. Then I can simply measure the KH at the start, and see if it drops over time. I would hope over a sufficiently short period in a new tank setup, there wouldn't be appreciable coralline formation or other calcium carbonate depositors to confuse the results.