Hi David,
Would have to get my notes out if I can find them after my days training. But was surprised yes there is a stage when the water turns to sulpuric acid but then needs to be balanced off. Resin holds the "h" and "o" so when you process the water through it the h & o's are relased giving you h2o.
All a bit complicated but yes was surprised that you can get sulphuric acid. To reverse the process of resin you will need to replace the h and o at the same time taking the ca etcc..
This is going over me head, will try and look at me notes if I can find them.