Wow, I have almost the identical issue. To save $$ on FROG dispensers I began floating Trichor a few years ago, and this year is first time I ever had algae that would not clear and 5 trips to the pool store I came across your site. I have always been compulsive about cleaning and sanitizing, but I hate to say not diligent about testing the water. It's been crystal clear and trouble free for years (until now). Time to better educate myself by grabbing knowledge from you all, who in my brief time on this site appear far more insightful and honest than any pool store anywhere... So my test results showed:
FC = 0
ALK = 80
PH = 7.2
CYA = 250
I just drained 60% (ouch$) and got CYA down to 120, abandoning Trichor in favor of Liquid Chlorine.
So my questions:
1) will the remaining crazy high CYA help stabilize the Liquid Chlorine indefinitely? Will the existing CYA now degrade on its own with no new Stabilizer added? Seems like I still need to get it down some more...
2) Starting to use Liquid Chlorine seems to mean I need to add Acid occasionally right? What kind of Acid and in what form?
3) Lastly, pool still looks really clean & new for 10 years old, but will soon will need a re-plaster and some reconditioning. Until then, this bout with algae has left some staining which scrubbed off clean on the exposed walls when I drained it down. But the algae stains under the water have not gone away yet. Once I dose it with Liquid Chlorine do you think the under water staining will come off?
I feel slightly silly having maintained my own Pools for almost 20 years and not knowing much of this, I guess I must have been doing something right being virtually trouble free, until now
Appreciate feedback from all! Cheers, Mike