Quote Originally Posted by Tom.B View Post
I just went out and had to backwash the sand filter. The pressure had jumped and there was no visible output from the jets. When I did, the water was very green coming out of the waste hose. Normal?
No, that's an indicator of algae. If you can, put a few tabs in the skimmer, which will raise the chlorine level in the filter, without raising it so much in the pool.


I actually have another question(s): What is the upper limit for chlorine with a vinyl liner? With a CYA of 55-60, I hesitate to run to the +SHOCK+ FC level to 30 as noted in Best Guess, much less 70ppm! Where should I raise it to and how long should I leave it there to kill off the algae?
Unfortunately, that's a question without a good answer. It varies from liner to liner, even within brands. I've been told that dark blue tends to be the color most susceptible to bleach-out, because of the pigments or dyes usually used.

Having a liner you're concerned about is an even better reason to try the phosphates. I probably should let you know I have entirely selfish reasons for wanting you to try phosphate removal: this is a perfect test case, for VALID use of phosphate removers:
=> You clearly have chlorine resistant algae -- the backwash is almost absolute confirmation of that.
=> You have a legit concern about 'mustard shock levels' of chlorine.
=> You're behaving predictably from our point of view and seem to testing reliably . . . so the 'data' we get from you is likely to be meaningful..

But . . . I really do hope it works. It would provide us a very useful additional tool with which to help people.