Quote Originally Posted by keastman View Post
But strangely, as soon as I approach 20ppm with free Cl, the pool turns that cloudy blue gray just shocked look and starts to clear in a few days and holds the CL overnight. but when I let the Cl fall off after 3-4 days and when the level starts dropping below 15, it starts to cloud up again and the yellow color of the dust on the bottom takes hold again..
The fact that it recurs when you lower chlorine is indicative of mustard algae. Do all these things:

1. Tell us how you are testing (if your CYA test results are NOT from a K2006, or other Taylor CYA test, we're going to tell you to get one!)
2. I've never said this before, but go your pool store, and see if they will test for phosphates. It's very unusual for mustard algae to recur at 20 ppm FC with only 55ppm CYA.
3. If you are not using your Quick-Clean flow director, cut it off, and EITHER
3a. Put MIP adapters on each riser, and then FIP caps on each adapter. Then pour 2 gallons of 1:10 bleach mix down each pipe. OR
3b. Connect each pipe to the supply with a 1/2 PVC section, so a small amount of treated water goes continuously through each pipe
[ Stagnant pipe are potentially dangerous. It's rare, but there have been cases of very dangerous pathogens accumulating in these pipes, and then during a maintenance failure, infecting a swimmer. ]
4. Let your chlorine drop, but put a trichlor puck on a flat plastic lid (don't let it rest directly on the pool surface) on a 'mustard algae' area. If the mustard algae does NOT develop around the trichlor, that's very indicative of algae rather than something else.