deep_blue,

Just wanted to clarify a few things in your post.

1) When you got rid of the SWG (and replaced the SS) did you also drain and refill your water to remove (most of) the salt? Do you know your current salt level?

2) I assume you didn't get a chance to try adding CYA in your SWG pool to see if that helped, is that correct?

As for your question about CYA with an indoor vinyl pool, I would normally say that using a small amount of it, in the 10-20 ppm range, would be beneficial for a number of reasons: it would reduce the "clean" smell of chlorine (not chloramines) since less chlorine would be volatized, it would reduce the degradation of swimsuits (fading and rubber deterioration), it would reduce corrosion rates even further, it would reduce the rate of production of disinfection by-products (DPBs). However, there are downsides: it makes shocking the pool to achieve breakpoint harder to do. Also, waste had added CYA to an indoor pool mentioned in this thread based on what I had suggested and ended up with an alage disaster, though other things went on as well including a larger than desired amount of CYA added and covering the pool. So I would feel really awful if you added CYA and had problems. I wish I could be more confident in recommending it -- my gut says a small amount would be OK, but it's hard to remove once you've added it.

As for the problems of shocking the pool to get rid of Combined Chlorine (CC), an alternative (regardless of whether or not there is CYA in the pool) is to use a weekly maintenance dose of non-chlorine shock (potassium monopersulfate, KMPS) which will oxidize organics before chlorine gets a chance to. This keeps CC low and also virtually eliminates DPBs. The downside to using non-chlorine shock is that it introduces sulfates into the water and it interferes with the Total Chlorine test, though there is an interference remover from Taylor, K-2041 for around $20.

Richard