Hey folks, I hope all of you are doing well! I've been super happy with our pool which came with our house purchased in Sept of '19. It had a lot of problems but I sorted it all out and it's been nearly perfect for the past year. I use the fantastic Pool Math app to keep track of everything. One thing I've struggled with is just getting my head around chlorine and the affects of loosing strength due to age. I've read everything I can find and I'm still missing how I'm supposed to calculate how much more LC I should be using as it gets older. I have a pretty good reliable source at a local grocery chain very close to my house. They store it indoors vs the large box hardware store all store theirs out side in the sun. That's great but they don't have a very fast turn around so, their supply is often quite old - upwards of 340 days. Because of that, I've been buying from Leslie's Pool Supply when they have it in stock. Recently, the local place had much newer stuff that was only 3 months old so I snagged a few cases. Here's what I'm dealing with now - I typically put 32 oz into a 20K gal pool. My CYA is stable in the low 40s. I keep the PH around 7.6 on average. Very recently, I'm noticing that the chlorine is not very stable but it's not predictable in how it's behaving. For example, I had an FC of 4.0 and put 64oz in (twice the normal). The next morning it was still 4.0. I put in 32oz and the next morning it dropped to 3.4. So I put in 96oz yesterday and today it's only recovered back to 4.0. Last year around this time as an example, I had FC of 3.4 and put in 32oz of LC and the following morning, FC was 7.2! Now one thing that has changed was I ripped out the Renaissance UV/Ozone unit because it sucked. Yes I know, you all told me. <grin> You were right. Could that be the difference? I'm just at a loss as to what is going on here.