Opener: I'm in the Dallas area and run my hose about 20-30 minutes each day during the summer to maintain a water level that keeps the skimmers from sucking air. I've got leaks around the tile and in the pool, have patched everything I find but still have to add water. Ultimately I will solve the leak issues with a pool remodel but until then I'm trying to keep chemistry stable. Recently the pool developed a dark color (black/brown/green) algae under the water line on most of the pool patch around tiles and cracks. Admittedly I've let the chlorine get low a few times this summer - noticeable by normal green algae on the sides of the pool which seems to be leaving a stain of sorts. I scrubbed around the tiles with a wire brush in case it is black algae (it was tough and I had to work at it), brushed down the sides of the pool and added liquid chlorine to SLAM.
About 35+ years old (I've had it two years)
Approx 25,000 gal
Originally gunite/plaster with fiberglass resurface and pool paint on the fiberglass
Chemistry before SLAM:
CC 0.0 to 0.5 (virtually undetectable)
CYA approx. 25ish
My CH and CYA are chronically low - likely due to adding water frequently. I use Tri-chlor pucks in a floating feeder and liquid chlorine to supplement as needed.
About 6pm I added 384 ozs of 10% chlorine - wanting to shock to FC 15ppm
7pm it was 11.6ppm and I added another 128 ozs
9:30pm it was 14ppm and I added another 128 ozs
Next day 7am it was 16ppm - mission accomplished
6pm (same day) it was 9.5ppm
The water is crystal clear (it never was bad - just had the dark algae)
CC is less than 0.5ppm
The days are sunny and hot in Texas. Is it normal though to drop 6.5ppm of FC in one day? Do I need to shock back to 15-16 and if so, how long should I maintain that level? According to SLAM instructions I'm in pretty good shape with clear water and CC less than 0.5ppm. I'll check OCLT tonight. I'm hoping to have a pool full of people this coming weekend so don't want the chlorine too high.
If I've done enough to combat the dark algae, what's the most important element of keeping everything else stable? Should I add stabilizer to bring up CYA so I'm not burning the chlorine so quickly? Is it important to bring up the CH? My PH and TA usually stay reasonable with minor tweaking of Borax and baking soda.
Thanks in advance.