As a volunteer at our neighborhood pool (165K gal, treated with 12% bleach and muriatic acid) I have learned enough over the years to be dangerous. But if you know a little more than the next guy you are labeled the expert around here, which is how I was invited to walk in to this situation at a friend's home.
His pool... 20,000 gal, sand filter, green with visibility to about 8 inches below the surface. My Taylor kit found no Cl, pH=7.3, TA=110, CH=230, and CYA a whopping 130 ppm. Lots of empty dichlor, trichlor, and algaecide containers from A&S Pool. He had just shocked the pool for the umpteenth time to attain 10 ppm Cl. Water level was above the skimmer. He said it has been green for a month and was not getting better.
My first thought was drain and fill to lower the CYA, but that's not practical for him. My second thought was that the high CYA was preventing treatment and possibly giving false test kit readings. And that I didn't want to add anything that would raise the CYA even more. So we put away all the white containers and went to the store for some gallon bottles of 6% bleach.
My calculations show that 3 gallons of bleach should raise Cl by 10 ppm, so I added 6 gallons on top of the Super Pool Treat he had just done with hopes of attaining 30 ppm overnight. Backwashed three times during the day which lowered the water to mid skimmer and improved flow rate significantly. He claims that he can now almost see the bottom -- some improvement --though I'm not sure I agree. But all the floating bugs are now dead.
Tonight I added 9 more gallons of bleach and hope to see some change in the morning.
Am I on the right track here? He's a bit in disbelief that my $2.00 bottles of bleach can do better than his hundreds of dollars of pool store chemicals. So my credibility is on the line for results. My intent is to add 9 gallons of bleach each night until the green turns brown. Any thoughts on how long that will take? Then reduce the bleach to 3 gallons each night while brushing, vacuuming, backwashing, and filling until his teen is exhausted from the work. And hoping that at some point the test kit readings will fall in line.
Is this a good plan? Anything to do differently?
Thank you for the sage advice I'm sure will follow.