A question about chlorine/cya chart

[nicnut45]

Everything I have read says chlorine should be maintained at 1-4 ppm. However, when looking at the chlorine/cya chart, the target fc column is always higher then 1-4ppm no matter how much cya is in your pool. What's the deal with this?
Right now my cya is at 70 and the chart says I need to target 8-10ppm fc. Is that going to be safe to swim in?

 

[Patrick_B]

Absolutely Safe.

The 1-4 limit is set forth by Government, and Industry standards that do not recognize the Chlorine Cya relationship.

 

[Divin Dave]

First, yes it's safe. If it weren't then the 10's of thousands or more of us who use a higher FC level in our pools would all be ill and we would not be maintaining our OWN swimming pools in such a manner.

The CYA combines with the Chlorine and produces bound up chlorine. This bound up chlorine is NOT active. Some of the chlorine added to the pool and in recommendations with TFP chart is not bound by the CYA. This unbound FC is the ACTIVE chlorine and is quite low. As the active chlorine gets used up, the Bound Chlorine releases from the CYA and become active.

The difference between TFP recommendations and Pool Industry recommendations is this.
The Pool Industry recommendation for FC is to kill bacteria - only, and then shock once a week to kill algae and to use algaecide.

TFP recommended levels will kill bacteria AND control algae but that be in relation to whatever the CYA is.

TFP recommendations are MUCH less expensive way to maintain your pool and it is safe.

The Pool Industry and Pool Chemical companies has known about this FC/CYA relationship for decades, but refuse to recognize that it's effective. If they did, they could not sell all of the chemicals that they do, and would go broke.

Here a couple of links to discussions on the subject. If you are curious about chemistry, then this should interest you and will explain the chemical processes.
Questions about Chlorine and CYA
Pool Water Chemistry

enjoy

 

[singingpond]

I think the active species of chlorine, the hypochlorous acid, is actually way lower than 2-3 ppm. To quote from chem geek (in the first of the linked threads mentioned in the above post):

QUOTE When there is 3.5 ppm FC with 30 ppm CYA and a pH near 7.5, 97% of the chlorine is bound to CYA, 1.5% is hypochlorous acid, and 1.5% is hypochlorite ion. END QUOTE

That's why a pool maintained with TFP recommendations will actually have a much lower level of hypochlorous acid than a typical commercial indoor pool, for example, which is usually maintained without any CYA at all. That commercial pool will have a quite low-sounding ppm of chlorine (they have to, in order to meet regulations), but it is not nearly as low as 1.5% of 3.5 ppm (as in chem geek's example for pool water with CYA).