Is a Pool Chlorine Level Above 10 PPM Unsafe?

[chem geek]

Just keep in mind that it is the active chlorine (hypochlorous acid) that attacks the swimsuit, not the Free Chlorine (FC) level. So when there is CYA in the water, the rate of attack is orders of magnitude slower. My wife experiences this effect every year when she uses an indoor commercial pool where the elasticity in her swimsuits gets shot after one winter season and her skin is somewhat flaky and hair frizzy until she takes a shower while in our own outdoor residential pool the swimsuits last for years and there aren't the same side effects with skin and hair. The main difference is that the indoor pool has 1-2 ppm FC with no CYA while our outdoor pool has 3-6 ppm FC with 40 ppm CYA which has an active chlorine level similar to around 0.1 ppm FC with no CYA. So the active chlorine level of the indoor pool is 10-20 times higher and oxidizes swimsuits, skin and hair that much faster as well.

The higher FC level does have an effect after you get out of the pool in that there is more chlorine in reserve so that it can keep reacting for longer as the water evaporates, but this effect can be minimized by rinsing the suits and is generally less important that the active chlorine level.

[JimK]

Thanks.

So a related question;

If I remember correctly, with my CYA at 80, the recommended shock level is 20. How much should I allow it to drop before swimming again?

[PoolDoc]

Women's fashion suits might want to wait till it's 15 or so. You just need to wait long enough for it to mix, so it's 20 all over, instead of 10 in most places and 40 near the returns. If you add it via bleach poured around the pool . . . 15 minutes should be plenty.

With a CYA of 80, 20 ppm is not going to have ill effects on swimmers.

[JimK]

Women's fashion suits might want to wait till it's 15 or so. You just need to wait long enough for it to mix, so it's 20 all over, instead of 10 in most places and 40 near the returns. If you add it via bleach poured around the pool . . . 15 minutes should be plenty.

With a CYA of 80, 20 ppm is not going to have ill effects on swimmers.

Thanks Ben. If I understand you correctly, if I follow my usual practice of shocking (I use cal hypo; pre disolved and poured throughout the pool) in the evening and letting the pump run all night, then it's OK to start swimming the next morning/day?

[PoolDoc]

Sure! It's also OK to swim that EVENING.

Using cal hypo? High calcium and SWCGs don't play well together.

Do you have a K-2006?
Do you know how to MANUALLY clean your DE filter?
Is your SWCG DOWNSTREAM of your filter?

If the answer to all those questions is yes, you might want to use an alternative method of dosing with cal hypo that will limit the calcium build-up in the pool. Meanwhile, you need to know where your calcium levels are at present.

[JimK]

Sure! It's also OK to swim that EVENING.

Using cal hypo? High calcium and SWCGs don't play well together.

Do you have a K-2006?
Do you know how to MANUALLY clean your DE filter?
Is your SWCG DOWNSTREAM of your filter?

If the answer to all those questions is yes, you might want to use an alternative method of dosing with cal hypo that will limit the calcium build-up in the pool. Meanwhile, you need to know where your calcium levels are at present.

I don't have that exact kit, but I have a few kits. One is a Taylor kit that I use to measure PH and TA (using R0014 reagent for PH, and R0007/R0008/R0009 for checking TA), another is a Taylor K1515-C (FAS-DPD Chlorine test), and a Tayor kit to test CYA level (using R0013 reagent), also a Jack's Magic Sequest kit, LaMotte test strips for borates, and most recently Aquacheck test strips for checking salt level (glad to report that the salt reading from the test strip reads almost the same as the SWCG display; gives me confidence my salt level is good). I did have a Taylor kit for checking calcium levels, but I had difficulty seeing the color change, so I returned it.

I do have calcium checked 2-3 times a season (May through Sept/Oct here). I checked my records since 2004 and calcium level has always been in the 200-250 range. I've never had any scaling on the salt cell or other parts since having the pool installed in 2004. It seems we get enough rain here to keep calcium levels from building too much. It's not uncommon that we will get enough rain in one storm that requires pumping excess water out of the pool. I haven't checked calcium yet this season (will do so soon), but I have no reason to think it will be any higher than usual. BTW, I've always used cal hypo to shock. Given this, is using cal hypo a problem?

I take the DE filter apart and manually clean it thoroughly at the end of each season. The salt cell is downstream (ie - after) the filter.

In my situation, do I need to be using an alternative method of dosing cal hypo (what is the alternative method??)?

Thanks again for your help. Your advice is greatly appreciated.

[PoolDoc]

If you've been using cal hypo, and have had stable chlorine over a full pool season, then no, it's not necessary to switch.

[CarlD]

I don't have that exact kit, but I have a few kits. One is a Taylor kit that I use to measure PH and TA (using R0014 reagent for PH, and R0007/R0008/R0009 for checking TA), another is a Taylor K1515-C (FAS-DPD Chlorine test), and a Tayor kit to test CYA level (using R0013 reagent), also a Jack's Magic Sequest kit, LaMotte test strips for borates, and most recently Aquacheck test strips for checking salt level (glad to report that the salt reading from the test strip reads almost the same as the SWCG display; gives me confidence my salt level is good). I did have a Taylor kit for checking calcium levels, but I had difficulty seeing the color change, so I returned it.

With the test kits you have, you have the equivalent of the K-2006. The FAS-DPD test in the K-2006 is the same as the K-1515-C you have. The pH test is the same, too. As is the TA and CYA tests. You are fine that way.