I was just reading this post, and I am as surprised as all of you as to why switching to bleach would cause this problem. I have found the complete opposite - cal hypo usually brings the stains out in my fiberglass pool. This is the way stains form in my experience. When there are any metals in the water - and metals come from dust, fertilizer, and who knows what else, even calcium is a metal, so even though the water doesn't test that metals are present in the water idoes not mean that aren't any. I never have metals show up in my tests, yet I get stains on my fiberglass pool if there isn't enough sequestering agent in the water no matter what I do. The fact that it is only on your return jets and skimmer is not a surprise to me, as these are made out of fiberglass (steps) and plastic. I read on a fiberglass website that fiberglass is magnetic, and it can draw out any metal that is in the water (I don't know if this is really true, but it may be why fiberglass stains and plates more than other pools). So if this is the case , then maybe it is why you only got stains on these parts of your pool. I know that the stain forms when the high chlorine reacts with high ph, and any metal that comes in contact with this solution will fall out. I can't answer why the calhypo never did this in your pool and bleach does, but it may have to do with the ph of the bleach. I have found that everyones water in the pool is different, and can react differently with different chemicals. There is just something a little different that is reacting with something else - So I understand why you want to know what it is. Sorry I can't help with that. Let us know if you do figure it out, so we can learn and help others.

You may just want to lower your ph to 7.2, and add a sequestering agent and see if the stains come off. If you do decide to do the ascorbic acid, you shouldn't need a lot, and you can start to bring up your chlorine right away. Just keep your ph low while raising the chlorine.

If you don't like the bleach, you can always swith back to what you were using before - if it ain't broke don't fix it