CYA

[Shellspool]

Ok, I think I'm having issues keeping my FC to shock level but I'm not sure.
When I do the OCLT the FC does not change. My water is clear and my CC is .5 but during the day, my FC will drop 3 ppm in 2 hours time. My CYA is 100 to 120. With a drop that much, is it safe to assume that there is something "growing" in the pool even though the OCLT tests clear?

 

[jblizzle]

If you pass the OCLT, then there is not likely anything in the water.

At high FC levels, it is not surprising to lose a lot of FC to the sun even with the high CYA. The CYA will only protect a % of the FC. With a CYA of 100ppm, I think it might be normal to lose 20-30% every day. If you are at 40ppm, that would be losing 8-12ppm each day.

 

[Shellspool]

So during the day when you are slamming, there is no way to know if you are losing FC due to sun or organics? So you just keep slamming (keeping FC to shock level) during the day until night fall and then do the OCLT? If that comes clean, then no more slamming?
Just trying to make sure that I understand it clearly.

 

[tim5055]

So during the day when you are slamming, there is no way to know if you are losing FC due to sun or organics? So you just keep slamming (keeping FC to shock level) during the day until night fall and then do the OCLT? If that comes clean, then no more slamming?
Just trying to make sure that I understand it clearly.

You have it, during the day when the sun is on the pool you are losing FC to UV radiation and organics. There are always organics in the pool a couple of leaves, things in the skimmer basket ect.

OCLT is only one of three things that have to be true to "pass" the SLAM:

You are done when:

1. CC is 0.5 or lower;
2. You pass an OCLT (ie overnight FC loss test shows a loss of 1.0 ppm or less);
3. And the water is clear.

If all three are OK, the SLAM is done

 

[Shellspool]

Ok but in an hour and a half my FC went from 39 to 29. Does this seem right? This morning I past all the slamming criteria but today I just wanted to make for sure so I brought it up to shock level of 39 and now it is already to 29. Should I keep slamming today and do the OCLT tomorrow morning? Water is clear and CC is .5. Thanks.

 

[jblizzle]

If you think you passed everything you are done. If you are unsure, do the OCLT again.

 

[ping]

Since you have said you already passed the OCLT and the two other criteria for the SLAM, I would let the chlorine fall for the rest of the day and run another OCLT tonight. The chlorine will be plenty high enough to run an OCLT as it is not required to be at SLAM level.