Mustard Algae problem or not?

[keastman]

OK Ben, I've been running my Free Cl between 25-29 for about 5 days with no CC and an overnight loss of 1-2ppm at most. The yellow has been gone for that period, only a small amount of clear dust on the bottom.
I'm about ready to stop the liquid chlorine and let the level settle while I continue brushing and vacuuming.

So, I tested my CYA tonight and it is down to 40 or just a bit under that when it was 50-55 when I started jacking up the Cl. My question is, will the high Cl levels interfere with the test or burn off CYA? I know you've written of the biofilm consuming the CYA, but I can't believe I'd have a viable biofilm at those Cl levels. There have been no significant rains or water added to the pool in this time frame. My pool does usually go down to "0" cya through the winter, so I figure that may be biofilm action.

[keastman]

Watermom, could you ask Ben to look at my last post and see what he thinks of the missing CYA. I've now stopped adding CL, still have the SWG off and am letting the Cl drop. It's come down from 28-18 in 48 hours with only the pump running. Water is still clear. I'm planning on switching back to 8 hrs a day on the pump and starting the swg again tomorrow. I will need to add more CYA again but am confused on where it went. I'm going to test it today and probably put a sock full in the skimmer. The pool is shaded for half the day.

[PoolDoc]

The CYA test isn't that accurate -- technically, if you get a reading of 50 ppm, both 40 and 60 are in the range of error.

When you add in the fact that high chlorine slowly breaks CYA down, and the fact that you may well have had some water loss during cleaning and such (typical, through of course, I don't know that it happened in your case)

[keastman]

Thanks,

I guess I'll continue to let the Cl fall and then add CYA to get back to the 60+ range for my SWG when I turn it back on. Then keep my fingers crossed that the yellow scourge doesn't re-appear.