Beforehand I'd been using ASW for 3-4 months, the reason I got some NSW is because the tank was looking bad. So, since the NSW came after the problem started it's not due to the NSW.
Just retested the salinity, it's a bit more like 1.025. Tested with a refractometer.
I'm thinking I'll leave the carbon out for good. No noticable difference from having it in.
Hmm, Yeah, I think I'll mix up a batch of ASW and do a big water change. I can't do a 50% though, not without dropping the water level past a couple corals and my anemone and draining my sump dry.