Disappearing CYA

[vinnygnj]

That probably is the post and I understand that small amounts need not be burned off with chlorine but I would also think that adding 6 PPM FC to a pool with 0.5 PPM CC will burn it off assuming that the CYA is at a low level.

As I said I never test for CC in the pool, only my spa but I guess in a situation like what I'm going through it might be worthwhile to test. But ...

... now more questions come to mind - Can CC really start accumilating if you are running high FC (8 - 10 PPM or more)? I would think not as anything under 1/10 of the chlorine you put in would be burned off (I am assuming that the pool started at 0 PPM CC and CYA is under 50). My pool was at 0 CC when I noticed I had no CYA.

How long do you need to keep a high chlorine environment? If you put in 10 PPM FC at 6 PM and you test at 6AM and have 6 PPM left, hasn't the chlorine done it's job. I always thought that as long as you have a FC residue that there isn't any more that the chlorine needs to do. (again CYA under 50). And wasn't the high chlorine in the tub burning off the CC as it was forming?

In my mind, a "shock" really isn't a specific quantity - it can be as low as 5 PPM FC or as high as 20 PPM FC, which is why I questioned the 15 FC figure for shock.

At this point with my pool not seeing a FC under 5 PPM since I started this post I would assume that any algea is dead. I actually put in 146 oz of bleach into my pool last night which yeilded 7 PPM chlorine added to what was there I was hovering around 11 to 13 PPM. I "shocked" the pool for the last time although I doubt there was a lot of CC in there.

[waterbear]

CC can accumulate, it depends on how much ammonia and urea or other organics are in the water. If you are killing algae then 0 ppm CC is a good indicator (along with the Fc holding overnight) that you have killed all the algae. If you do not raise the FC high enough to destroy all the orgainics in the water you will still have CC left.

Your example of putting in 10 ppm FC at 6 pm and losing 4 ppm overnight indicates that the chlorine is fighting something in the water and you need to continue to shock until the FC holds overnight when UV degredation of chlorine is taken out of the equation. This is a basic of the BBB method on here. Just read the posts!

"Shock" is really raising the FC high enough for the level of CYA in the water to insure that there is enough 'active' chlorine to do the job and it is not bound up with the stabilizer in the form of chlorinated isocyanurates but is in the form of hypochorous acid.

It is a combination of having no CC and having your FC levels hold that indicates that you do not have a chlorine demand in your pool. If this is not the case you need to continue shocking and possibly try shocking to a higher FC level. It is also important to keep the FC at shock level by adding more chlorine at least a few times a day.