Could this be algae or dirt/pollen?

[chem geek]

Well, if your chlorine is holding, then it isn't breaking anything more down and if the dust or algae or whatever it was is gone, then it is probably killed and filtered or broken down. If it was truly red (the pictures at the start of this forum look more green/yellow to me and that's more like mustard/yellow algae), then this could either be non-algae like dirt or could be a red algae (there is that type of algae, but it's usually not found in pools as far as I can tell).

Anyway, it does sound like you've solved your "red dust" problem. On the CYA amount, I am surprised that 60 ppm CYA makes that much of a difference compared to 30 ppm CYA. In theory, it would only increase the half-life of chlorine (in direct noontime sun) from around 6 hours to 7 hours which isn't that much of a difference. Of course, whatever works for you is what is best.

Let your chlorine drop to "normal" levels but keep it as suggested at around 6 ppm FC or so minimum (at your current 40-50 ppm CYA level) and see if this stuff returns. If it does, then you can try shocking to higher levels (20-25 ppm) as I mentioned in my earlier post.

Richard