I've had my house w/in-ground pool for almost 2 years, started following TFP shortly after moving in, and haven't had any issues. Lately, I've been dealing with a light growth of light green surface algae on the walls of the pool in certain places - primarily on steps, and walls far away from my returns. Brushing (which I do pretty regularly, but not daily) removes most, but not all of the surface algae. The pool water continues to be clear - you could read a book laid on the bottom, or count the tiny specs of aggregate in the finish. And the pool is still blue, not a greenish hue. This is why I think it's really just surface algae - whatever is in the water column seems to be killed and filtered out quickly.
I've been dealing with this for a few weeks now. Brush, dose chlorine, pool looks clean for a few days, but then the algae patches return. Lather, rinse, and repeat. Last weekend my wife and I scrubbed every inch of the pool, and I dosed it good with chlorine. Maintained it at recommended levels (usually target 7ppm) during the week. On Friday, before heading out of town for Mother's Day, I brushed the sides again, and added a gallon of chlorine to put my FC at 10. Two days later, I come home to FC of 2, and light algae on the walls in the regular spots. Historically, my pool consumes only about 2ppm FC per day, so I would say my consumption is trending higher than normal.
Here were my numbers from this evening (TF-100):
CC: .5ppm (barely any pink, cleared in 1 drop)
CYA: measured 40-50, call it 50 (I deliberately keep it here due to strong sun)
Temp: 83 (ish)
I want the pool clean for Memorial day, so I've decided to hit it with a SLAM. Right thing to do? Heck, chlorine is cheap enough - $2.20/gal for 10.5% at my local pool store.
I started with enough muriatic to lower the pH to about 7.3. Gave that a half hour to mix, and added 2 gallons of chlorine, which I estimated to bring FC to a target shock level of 16ppm. Gave that another half hour and measured 17, all good there. I'll check it again in the morning and see what my overnight loss is.
Bottom line, if I pass the OCLT (not necessarily tonight), will I be able to break the cycle of recurrent surface algae?