This thread is extremely interesting to me, in part because it is bringing back long forgetting memories of moles, molecular weights, and similar, personally-unused concepts and, in part, because it does present evidence that supports the possibility that Equilibrium can cause problems. But I remain an agnostic on that.
One question that I have is, what happens to the SO4 when it splits from the CA? I suspect that it undergoes further changes, rather than just sinking into the substrate. Some of it is undoubtedly absorbed into plant tissue; perhaps some combines with other chemicals and becomes insoluble. I don't know.
While walking through swamps I've often encountered large amounts of H2S. (It can be easily identified without expensive lab equipment.
I wonder if high sulphates in the water by themselves are responsible for this or if there is some other process involved that grabs whatever sulphur is available to combine with the hydrogen. I don't know that, either.
It would be interesting to conduct an experiment with two natural tanks with anaerobic substrates and water with low sulfates. CaSO4 would be added to one and the amount of H2S measured. The point at which H2S becomes a threat would also have to be predetermined.
Bill