This is only the second time I've had to shock the pool and it's taking much longer than the first time. I'm now on day 12 and the pool is still greenish. Before starting the test results were:
Before starting I cleaned out all the leaves and debris and back washed the filter. There was a ton of pine tree pollen on the surface and even more oak tree pollen on the bottom. Next I added 1L of HCL to bring the pH down to 7.2 and enough 6% chlorine to to get 13 ppm which is what the chlorine/CYA chart said was needed for a mustard algae shock.
When I started the pool was a very pretty forest green color. After two days it turned to a distinctly yellowish-green. After three days it was a greenish white and I raised my chlorine target to 20 ppm. It is still a greenish-white on day 12. The pump has been running 24/7 since starting and I've had to back wash 3 times.
One big difference I've seen is that chlorine consumption is much lower this time around than it was the first time. The last time I used 60 gallons of 6% bleach in 6 days and the pool was clear. Now after 12 days I've only used 53 gallons of 6% and the pool is still greenish. The target level of 20 ppm is the same I used last time when the starting CYA number was 40. I've been watching the over night CL loss and it rarely gets over 1.5 ppm. Also I have not detected any combined chlorine and last time the CC jumped up to 2 - 3 ppm after the first day.
Is this normal or could something else be going on?