Is a Pool Chlorine Level Above 10 PPM Unsafe?

[JimK]

So it's apparent that chlorine would have to be very high to hurt us, but what about our bathing suits? For example, if my CYA is 80, what would the maximum FC level recommended to avoid destroying my bathing suit?

[PoolDoc]

No good answer to that: the most expensive women's suits are almost completely intolerant of chlorine.

I can tell you that very expensive women's suits are worse than moderate ones, and that suits with elastic (Lycra) are much worse than nylon board shorts or guard suits . . . and that 100% polyester competition suits last forever. But other than that, you have to experiment. However, if you are asking the question, I'd recommend separating your family's suits into "swimming suits" and "showing off suits". If you do that, you'll likely end up with the more chlorine resistant ones in the swimming pile.

I have some OLD (20 year old) data on grades of Lycra used in competition suits . . . and I can tell you that, at least back then, the most common Lycra elastic was sold on the presumption that women would 'slip and dip', not swim. I think the life expectancy was something like 5 hours at 3 ppm - and that the suit would last the summer. They didn't consider or test stabilized chlorine solutions.

[JimK]

No good answer to that: the most expensive women's suits are almost completely intolerant of chlorine.

I can tell you that very expensive women's suits are worse than moderate ones, and that suits with elastic (Lycra) are much worse than nylon board shorts or guard suits . . . and that 100% polyester competition suits last forever. But other than that, you have to experiment. However, if you are asking the question, I'd recommend separating your family's suits into "swimming suits" and "showing off suits". If you do that, you'll likely end up with the more chlorine resistant ones in the swimming pile.

I have some OLD (20 year old) data on grades of Lycra used in competition suits . . . and I can tell you that, at least back then, the most common Lycra elastic was sold on the presumption that women would 'slip and dip', not swim. I think the life expectancy was something like 5 hours at 3 ppm - and that the suit would last the summer. They didn't consider or test stabilized chlorine solutions.

I see. So when shopping for a "pool suit", I should look for nylon or polyester and try to minimize/avoid lycra. We're too cheap to buy expensive suits, so guess we should be fine with the recommended "best guess" levels.

[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?