Help me please with my cya problem

[Me...]

One answer is Ozone. And I constantly praise a GOOD system. Also I believe the German DIN standard requires it. Maintained I think at a residual which allows no more than .4ppm within 6" of the water surface. The water is pulled from the pool, 100% ozonated, Superchlorinated, Dechlorinated, and enough Ozone reintroduced to maintain that .4ppm. They are very short on water over there and we do not think we are, so they will spend the bucks to get good water. We drain and flush and refill and consider seeing the bottom of the pool constitutes good water.

The above proceedure will kill and oxidize almost everything and do it with very little to no THM's created. The chlorination finishes the job and the Ozone will be the residual but it is VERY expensive. We typically *attempt* to treat 20% to maybe 30% of the water here. And many times its a haphazard job. I won't start or my fingers will nubs.

These days I find myself hoping the UV systems actually turn out to be useful. I can already see where I can punch holes in them but ............. time will tell. I love Ozone and god knows there are many terrible systems out there.

[chem geek]

As I had written in an earlier post in this thread, the German DIN 19643 standard used in Europe has the FC between 0.3 and 0.6 ppm in order to reduce disinfection by-products. The standard also uses activated carbon to remove chloramines during filtration, but that also removes chlorine that must be added back. The use of ozone is optional and if done then the chlorine range is from 0.2 to 0.5 ppm. Ozone is NOT the residual in such systems -- it is still chlorine re-injected. The standard 19643-2 uses combined adsorption, coagulation, filtration and chlorination. 19643-3 adds ozone to that mix. 19643-4 also uses ozone but uses multi-layer filtration instead of adsorption.

The reduction in disinfection by-products comes from a combination of low active chlorine levels and from removal of organic precursors (coagulation and filtration) and removal of chloramines (adsorption, which also removes chlorine). Ozone assists in the oxidation as an option.

The low FC level has to be carefully maintained since it can rather easily get used up under heavy bather load or an excess of sweat or urine (think of children urinating in the pool, for example). 4 ppm FC with 20 ppm CYA would be equivalent in active chlorine level as 0.2 ppm FC with no CYA but would have plenty of reserve capacity to not run out. Of course, one could not use this approach economically with German DIN 19643 since all chlorine is removed on each filtration pass.

[Me...]

Ooops. You are right, chlorine residual. I was typing with the brain in neutral. The method does produce excellent water though but it is a more expensive method than we normally use here. However if you look at the costs from every angle including health issues and water waste it might look quite a bit better.

[chem geek]

In an outdoor pool exposed to sunlight, the method would be more expensive in residential pools, but would probably be OK in high bather-load commercial/public pools. At 0.4 ppm FC and no CYA, the chlorine loss would be around 0.2 ppm FC every 30 minutes so with 6 hours equivalent of direct noontime sun that would be 12*0.2 = 2.4 ppm FC per day chlorine loss (just from the sunlight and not counting normal loss from oxidation of things in the water) which is higher than the 1-2 ppm one usually sees in residential pools. Of course, using a pool cover opaque to UV would significantly reduce such losses.

[Jmrcjc]

I have purple stuff on the bottom and sides of my pool I am thinking it is cya but how do I know for sure. Last week my cya level was tested at 50. What do I need to do. Any help would be appreciated