Yes, that could well be true. I mostly wanted to see if it was something specific to coralline, but it may be something that inhibits calcification in general, and in that case, the culprits ar usually phosphate (organic or inorganic), other organics, low alkalinity, low calcium, low pH, or some combination of all of those.
I'd boost the calcium and magnesium, but that may not solve the problem. Let us know what happens.
