Quote Originally Posted by CarlD
Seriously, SERIOUSLY WRONG assumptions!

Wow! If that CYA is right you should NEVER let your FC go BELOW 8ppm, and probably not below 10ppm. It's binding up so much chlorine that you need to run much higher levels just to keep your pool sanitary.

But since your FC=7.8 and your TC = 10.4, that means your CC is 2.6ppm. That means you are fighting something and need to shock your pool RIGHT NOW! With a CYA of 172, the shock level you need to go to is 25ppm of free chlorine. You need to keep it there until Total Chlorine is no more than Free Chlorine, which will mean that Combined Chloramines (CC) is 0.

You are on the brink of an algae bloom. Once you get that under control, you have two choices.
1) Run a high CYA/High Chlorine pool. That's not a big deal but you need a FAS-DPD test kit to test the chlorine at the higher levels and you need to stay on top of it. You are done using chlorine tablets and powders--they are what put you in this fix because they have been dumping CYA into the water. Use bleach or liquid chlorine.

2) lower CYA to reasonable levels. There are only 2 ways to do this, but the better is to drain most of your pool and refill. If you drain 1/2 and refill, your CYA will still be 85--very, very high. If you drain 3/4 of the water, the CYA will be about 45--at the high end of the normal range of 30-50ppm. Then again, you are done with tabs and powders and need to use only bleach or "liquid chlorine" to chlorinate.

Have another pool store confirm those numbers. The CYA and CC are SO high that I'm hoping, beyond hope, that it is a bad reading. But probably not.
Wow is right. I had no idea it was in that condition. It looks great. Obviously I would prefer not to drain the pool. What happens if take about 12 inches out and refill then just let it sit and monitor? How long will it take for the CYA level to drop? Am I correct in that by using the tablets and having the chlorinte high I was also adding to the CYA level?