Basic question re: Cl warnings >4 on product labels

[shacke]

I am adjusting my pool management based on the information I am finding in here, particularly from pool school and the pool calculator.

Here is my question based on what manuals and labels are telling me:

1. Based on my current CYA level, pool calculator suggests 4-8 ppm of FC with shock level of 16. All labels on the chlorinating materials I own, specifically bags of cal-hypo and jugs of liquid chlorine (which I plan to finish off and go with straight bleach btw) state that it is unsafe to swim until the FC drops to 4 again. Is this warning akin to the (bogus) need to cook your meat to 185 degrees? Is there a gov't mandated statement on the safety of FC levels over 4? Do they not take into account any pool having CYA binding much of the chlorine (although the bags of shock recommend CYA in the pool?

2. The recommended FC level in my goldline aquarite SWG manual is 1-3ppm and that is along with a recommendation that a CYA of 80 is 'best'. That makes no sense to me AT ALL.

So there is a disconnect between the pool forum(s) and commercial preparations and products.

What is the scoop? :?:

Thanks so much!

Evan

 

[JohnT]

Yes there is a disconnect. The missing information is the chlorine/CYA relationship. They treat chlorine as if it is as effective at CYA=0ppm as it is at CYA=100ppm

Note that CYA levels for SWCGs are different, and the recommended level should be followed.

 

[chem geek]

You will never see any chlorine product say anything above 4 ppm FC for pools or 5 ppm FC for spas because those are the limits set by the EPA. Unfortunately, this standard is set based on drinking water standards assuming quarts of water drank every day. The standard also does not consider the effect of Cyanuric Acid (CYA) on the active chlorine concentration -- the component that does the sanitizing and oxidation (i.e. the real work). They also do not consider that there is virtually no CYA skin absorption so likely to be minimal from chlorine bound to CYA.

So while labeling and instructions cannot say anything about higher chlorine levels due to the FIFRA rules from the EPA, many states and local governments allow for higher chlorine levels in public pools and are written into their standards, many allowing up to 10 ppm FC. So even between the government agencies you've got inconsistency.

 

[shacke]

I suspected something legal was behind it. Thank you for the detailed and very informed responses. It really helps.

 

[Richard320]

Regulatory gibberish. I can buy a gigantic bottle (a small drum, really) of 200mg ibuprofen at any drug store, but I can't take more than 2 at a time. Unless my doctor prescribes it, then I can buy 800 mg tablets. Get real.

 

[shacke]

So the follow up question is this. Is there an unsafe level, when accounting for CYA, above which there should be no bathers? eg, in my pool the shock level is 16 and it would take a good long while for that to drift down again to the 4-8 maintenance level.

I want to make sure I am not endangering the kids or pets. Me? I don't care much

Evan

 

[svenpup]

Anything below shock level for a given CYA is OK, but you wouldn't want to swim while you are actually in the process of shocking.

 

[Isaac-1]

One thing to keep in mind is those instructions on the backs of the commercial products have not changed in 30+ years.

Many still just suggest having "some" stabilizer in the water with little effort to quantify it or even mention the concept of over dosing it.

Most of the better test kits you can find on local store shelves don't even offer a test for CYA and those that do (mostly strips) have such crude resolution to be nearly useless.

 

[chem geek]

So the follow up question is this. Is there an unsafe level, when accounting for CYA, above which there should be no bathers? eg, in my pool the shock level is 16 and it would take a good long while for that to drift down again to the 4-8 maintenance level.

I want to make sure I am not endangering the kids or pets. Me? I don't care much

Evan

Evan,

As svenpup wrote, anything up to shock level is generally considered to be OK on this forum. The normal shock level (which is an FC that is roughly 40% of the CYA level) is roughly equivalent to a pool with 0.6 ppm FC and no CYA. Even at the higher yellow/mustard algae shock level (which is an FC that is roughly 60% of the CYA level) this is roughly equivalent to a pool with 1.4 ppm FC and no CYA. (Even assuming 90ºF water with a worst-case temperature dependence these are equivalent to 1.1 and 2.1 ppm, respectively.) So these are generally less than found in most indoor pools that don't have any CYA in them. It's not something you'd want to swim in all the time unless you don't mind the extra wear on swimsuits, skin and hair, but it's not unsafe for infrequent exposure. Inhalation exposure, including disinfection by-products, will be proportional to these lower effective FC equivalents with no CYA.

Since there is minimal skin absorption of CYA, so likely to be minimal absorption of the chlorine bound to CYA, the main risk for the high FC is direct ingestion of the water through the nose and mouth. The EPA limit of 4 ppm FC per day assumes 2 quarts per day of drinking water so you would not want to drink large quantities of pool water on a regular basis. Probably the worst practical exposure would be gulping the water into the lungs but again would mostly be a problem for frequent occurrences.

So what is a truly unsafe level? Very hard to say, but would be a lot higher than one would normally achieve when one has CYA in the water. It's a lot easier to get to levels that you smell and may be irritating when there is no CYA in the water. 20 ppm FC with no CYA gives a clear eye irritation in rabbits, for example. Basically, you will get smells and irritations long before you reach anything that is truly unsafe from a one or few time exposure.

Richard

 

[shacke]

Thanks, Richard for the detailed and very informative response.

Evan