What chlorine level to shock -- now that half my CYA is gone

[Watermom]

Sequestrants keep metal in suspension, the Culator will remove the metals. Also, skimmer socks can be rinsed out and reused over and over again. Just a little info.

[JimK]

Sequestrants keep metal in suspension, the Culator will remove the metals. Also, skimmer socks can be rinsed out and reused over and over again. Just a little info.

Thanks. I'll keep that in mind when I'm ready to tackle that.

[PoolDoc]

@Watermom: good catch; thanks!

[JimK]

Ugh...still losing too much FC overnight (about 6ppm).

Although there is no sign of algae, my concern is if I set my SWCG to maintain 5-6ppm during the day like I normally do, then when the system shuts off in the evening (I normally run the pump about 10hrs a day) all the FC will be gone by morning.

So this evening I hit it with another 7 jugs of CL bringing FC back up to a little over 30ppm. Hopefully this will knock out whatever is eating up the FC. I'll keep checking CL levels twice a day (morning and evening) to see if this does the trick.

[PoolDoc]

I think we need to do a better job of explaining to pool owners the options for avoiding any bacterial growth over the winter! It doesn't effect everyone equally, but for many it causes some painful start-up problems.

Hopefully, we can help you avoid this next year!

[JimK]

I think we need to do a better job of explaining to pool owners the options for avoiding any bacterial growth over the winter! It doesn't effect everyone equally, but for many it causes some painful start-up problems.

Hopefully, we can help you avoid this next year!

Most years it hasn't been a problem. But now and then the issue pops up.

A quick update:

Last night after checking FC level I shut down the pump (up until now it's been running 24/7). This morning's test showed no FC loss overnight.....yea! I don't know if that last shock treatment did the trick or turning the pump off last night had something to do with it. Does aggitation cause FC loss?? I know in another thread some time back there was a discussion about whether using one of those magnetic stirrers when testing CL altered the results as apposed to just swirling by hand. Was there any conclusion on that?

Btw, the first night after the last shock it lost 11ppm overnight.....however we did get some heavy rains, so that may have contributed to the loss.

So once the FC drops to normal levels, I'll start up the SWCG again and see if FC stays steady, day and night.

[PoolDoc]

Does aggitation cause FC loss?? I know in another thread some time back there was a discussion about whether using one of those magnetic stirrers when testing CL altered the results as opposed to just swirling by hand. Was there any conclusion on that?

Agitation does not cause chlorine loss, in and of itself.

But, apropos of your situation, filters can accumulate massive bacterial growth. Judging from the odors I've encountered when opening filters in spring, I would guess that what's happening is anaerobic decomposition of oils and films on the sand - which is a good thing, I suppose.

However, the residual bacterial and decomp products could definitely create a chlorine demand.

-- This is a new idea for me. I've known about this, but never considered it. I have encountered 'greasy' sand on multiple occasions, and have considered that using the skimmers to add chlorine prevents this. But I'd never thought about 'cleaning' filters with bacterial digestion -- frankly, I'd never gotten past 'gagging' at the odor and black slime! --