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

[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! --

[JimK]

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! --

Now that the pool itself seems fine would you suggest that I backwash the DE filter and recharge to get the "spring cleaning gunk" out of it? When we vaccumed it we did it through the filter and not to waste (only raised pressure 1-2 pounds) because vaccuming to waste uses up so much water.

[PoolDoc]

Actually, I'd recommend you OPEN the filter, and wash it out. Backwashing never fully cleans a DE filter.

I just looked up the manual for that Hayward filter. It's a big filter case, and they are somewhat tricky to re-assemble. You have to be careful to get the O-ring clean and aligned, the O-ring groove clean, and the case in place, without bumping the O-ring. Then you have to install the band and torque it into place.

It works better if you use a machine hammer to tap the ring as you tighten:
1. Snug the bolt up.
2. Starting in the position 180 degrees from the bolt, use a machine hammer to tap the ring lightly, moving from the opposite position evenly to the bolt. Do this on both sides.
3. Then tighten the bolt some more, and 'tap' again.
4. Once you are nearly fully torqued, tap the ring again, and then fully torque the bolt.

If you don't have a torque wrench, here's a well-rated, but inexpensive one. Please note that 150 inch-pounds is specified, but that that is equal to 12.5 foot pounds. (Which actually seems light to me -- but I have enough experience to go by 'feel', and adjust that way.)

Anyhow:

Hayward Pro Grid Manual
Neiko 3/8-Inch 10-80 Foot-Pounds Automatic Torque Wrench

[JimK]

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! --

This post made me think of something. When closing for the winter I drain and take the DE filter completely apart and thoroughly clean the grids, tank, etc., so I don't get any bacteria/gunk buildup over the winter.

I've always done this because I was told if you let the DE sit over the winter and dry out, it can get like concrete and be very difficult to clean out. It didn't occur to me that another issue would be increased CL demand from all the bacteria/gunk buildup that would occur.

Thanks for bring that up.

[JimK]

Just a final (hopefully) recap;

Lost about 40ppm CYA over the winter.
Went through 25 gallons of 8.25% bleach before it would hold FC level overnight.

Now where's the heat!