I have been having a Edit: PM sent, Butterfly problem keeping the silly OTO anywhere near yellow.
I drug out the K-2006 and ran the CYA (disappearing dot) test 3 times - twice using one bottle of reagent, the third with the unused bottle.
In all cases, there was little or no cloudiness - I could fill the entire tube and the dot was visually unobstructed.
I seem to be out of CYA in the garage, so off to the store - but...
HOW did the CYA disappear? Is that reagent volitile to the point that 2 year old stuff is inert?
I now have mustard algae, and am using something Home Depot sells as 20,000 Gallon Shock - 2.25 oz (1/8 of a cup) is supposed to raise FC by 1 ppm in 10,000 gal.
I just dumped 7 oz. in and ran the pump for 2 hours - the OTO is off the scale, but the south wall still shows yellow (I had just wire-brushed it before adding the HD stuff.)
If it turns out I have been trying to chlorinate 15,000 gal in the Sacto sun (105F) with no CYA, it would explain a lot.
It would NOT explain the complete lack of CYA (was 50 a year or so ago). We have a drought (you may have heard), so rainwater is not the culprit.