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

[JimK]

Well, I thought it would be smooth sailing from here, but this morning's readings threw me off.

Last night:

FC 9
CC 0

There was a 4ppm loss of FC during the day yesterday (seems normal since I hadn't started the SWCG yet).

This morning:

FC 2
CC .5

I certainly didn't expect a FC drop of 7ppm overnight!

Last night I did take a full set of measurements (I can post those if needed), and added the following:

1 box borax (pH was reading 7.2 so I threw in the last box of borax I had)
3.25 lbs of stabilizer to bring it up to the recommended 70-80ppm
100 lbs of salt
2 quarts of Jack's Magic Purple Stuff (if I don't use this I get staining...I'll address this in another thread at another time)
1 quart of polyquat (60%); I do this every spring for insurance while getting CL levels stabilized.

Could anything I added last night explain the big FC drop?

This morning I started up the SWCG and added 2 jugs (121 oz each) of 8.25% bleach. Also, when starting up for spring I always run the pump 24/7 until everything is balanced and stable....don't know if this matters in this case.

[PoolDoc]

I've pretty much given up explaining everything I see happen in pools. Sometimes, years later, I find out what was going on, but mostly not. Weird stuff happens from time to time in pools, and unless your goal in life is to be an amateur chemical detective, it's better to let it go UNLESS it's causing a real problem. Who knows, if you have a dog, maybe this:

is the explanation.

If you are regularly adding Jacks Magic, you may want to get and use some CuLator packs. They are not effective for quick clean-up, but they do continuously remove metals from the water, unlike products like Jacks Magic which work temporarily to keep it soluble. If you do get some, do NOT throw them away monthly, like the company encourages. They are not 'used up' till badly discolored OR fouled with goop. Keep one in your skimmer, but use a skimmer sock on top to protect the pack from 'goo'. You can also just chuck them in the pool. The more you have, the more effective they'll be. Just don't put them where they will get ruined with greasy dirt. (So, don't put them in a chlorine floater, where lotion and suntan oil can foul them.)

1 ppm Culator
1.5 ppm Culator, sold by Amazon
4 ppm Culator, sold by Amazon
Poolmaster 16242 Poolmaster Skimmer Basket Liner

[Watermom]

I bet it was the polyquat that caused the drop in FC.

[JimK]

I've pretty much given up explaining everything I see happen in pools. Sometimes, years later, I find out what was going on, but mostly not. Weird stuff happens from time to time in pools, and unless your goal in life is to be an amateur chemical detective, it's better to let it go UNLESS it's causing a real problem. Who knows, if you have a dog, maybe this:

is the explanation.

If you are regularly adding Jacks Magic, you may want to get and use some CuLator packs. They are not effective for quick clean-up, but they do continuously remove metals from the water, unlike products like Jacks Magic which work temporarily to keep it soluble. If you do get some, do NOT throw them away monthly, like the company encourages. They are not 'used up' till badly discolored OR fouled with goop. Keep one in your skimmer, but use a skimmer sock on top to protect the pack from 'goo'. You can also just chuck them in the pool. The more you have, the more effective they'll be. Just don't put them where they will get ruined with greasy dirt. (So, don't put them in a chlorine floater, where lotion and suntan oil can foul them.)

1 ppm Culator
1.5 ppm Culator, sold by Amazon
4 ppm Culator, sold by Amazon
Poolmaster 16242 Poolmaster Skimmer Basket Liner

Thanks Ben. There's no sign of algae or anything, so as you suggest I'll just write it off as a quirk and move on.

LOL.....no dog here. 99.99% of the time it's just the two of us using the pool.

Once I get CL levels stabilized and the SWCG set, I'll look at addressing the metal issue. BTW, last year you had me do the bucket test for metals. Despite the results being negative for metals, the stairs starting staining again when I stopped adding sequest (6 oz a week after the initial does of 2 qts does the trick).

My hesitation with the Culator is cost. At least if used as recommended, it costs more to use the Culator than the sequest, not to mention that for some time I'd have to use the sequest and the Culator together, increasing cost further. Then add the cost of the skimmer socks, which would likely get clogged quickly and require frequent replacement due to all the nearby trees. So it seems that going with the Culator would cost more and add more maintenance than just adding the sequest once a week. I would like to persue this discussion further, but I'll start another thread for that at a later date when I'm ready to tackle it.

I bet it was the polyquat that caused the drop in FC.

Now that you mention it, I do think I remember reading that polyquat increases CL demand? If so, I think that may be it. Thanks for pointing that out.

[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!