I'm new to the site, had pool guys managing my pool until I retired a few years ago. They just added trichlor pucks and algaecide once in while and so that's what I did, just checking with test strips. After several summers of no algae ever, not even using any algaecide, I started to have problems with it three years ago. The guys at the pool store said everyone was having problems and so I used commercial shock products and algaecide. This year I got tired of all the chemicals and looked for an alternative. After studying TFPC, I think I have two problems. The first is a CYA of 110 (used a 1:2 dilution). I'm trying to delay changing out the water in the pool until September so we can use it without interruption and then I have time to get it rebalanced before closing.
Second, I noticed that when I sweep the pool (almost every day this year, trying to prevent algae), I find slimy flakes around my pool light every day. I realized that I had the bulb replaced the spring before all the problems started. It was replaced when the pool was opened that spring, and now that I think about it, I'm sure the pool wasn't balanced and completely clean yet.
So yesterday I opened up the light fixture and, wow, there was a lot of thick beige slime. Not sure what type of algae is that color, but there was lots of it. I added a copper algaecide to try to keep what was released into the pool from taking hold and then today started a SLAM. (BTW the pool has been perfectly clear after some initial work at opening, and but was murky after the light fixture was opened. It was clear again this morning.
I am sold now on nothing but liquid chlorine, and bought 18 jugs of 8.25 % hoping that would be enough. First, I read on a thread that chlorine works better at lower pH, so I added dry acid to bring the pH to 7.1. (My TA is about 125 so lowering it by adding acid is a secondary reason for this.) The reference table for FC levels said I'd need 39 ppm for the SLAM, but the calculator said 26 for shock. I used the higher number, adding 10 jugs of chlorine. Using 10 ml for the test sample and a dilution of 1:3, I got 38 for my initial level after 1 hour of circulation. Close enough. Then got about an inch of rain in a heavy storm. Checking an hour after the rain stopped, the level was 36. Added another jug of chlorine. After a couple of hours the FC was 34. Added 1.5 jugs and will check again before bed so I can see how much I lose overnight. I am doing all of this with the light fixture open. I don't want any algae hiding in there.
I have two questions:
1) Why is it OK to swim in the pool with such high levels of free chlorine? I guess the chemist in my wants to understand what the CYA is really doing that I can have 39 ppm in the pool and not have it be very irritating.
2) Am I on the right track? I'd really like the advice of all the experts out there. I have a chemistry degree, but that doesn't mean I understand all of this. Below is the most recent test results from before I started the SLAM.
TA 125 (I corrected for high CYA the reading was 160 - .3(110) ~ 125
FC during SLAM has not dropped below 34, and I am adding 8.25% bleach to keep it at 39. Will do OCLT tonight.
Thanks! I am so glad to have found this site!