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The stability of saltwater oversaturated with calcium carbonate depends from many factors, phosphate concentration and organic compounds amongst others. This is the reason why freshly prepared saltwater is so much more prone to the formation of precipitates. You can split a batch of freshly prepared saltwater in two and put the one halft into a cycled tank and the other half in a sterile tank and you will get precipitates only in the sterile tank.
The role of phosphates can be seen clearly when phosphate concentration gets locally or generally reduced. In local reduction by bacterial activity, promoted by organic carbon dosing, i. e. the bottom gravel may clump or even solidify from calcium carbonate precipitates.
Sinking alkalinity after phosphate removal may not be a sign of increased coral growth but only of increased precipitation. If this is the case it makes no sense to counteract it with increased dosing.
So it is hard to give recommendations for a tank at the limit of calcium carbonate saturation. I recommend trial and improvement. You seem very skilled to me and I am quite sure you will find a good solution.
The role of phosphates can be seen clearly when phosphate concentration gets locally or generally reduced. In local reduction by bacterial activity, promoted by organic carbon dosing, i. e. the bottom gravel may clump or even solidify from calcium carbonate precipitates.
Sinking alkalinity after phosphate removal may not be a sign of increased coral growth but only of increased precipitation. If this is the case it makes no sense to counteract it with increased dosing.
So it is hard to give recommendations for a tank at the limit of calcium carbonate saturation. I recommend trial and improvement. You seem very skilled to me and I am quite sure you will find a good solution.