Chemical Confusion - Can't Get A Free Chlorine Reading

[CarlH]

After finally getting a very dirty pool clean, I'm having water problems - specifically, not getting any free chlorine reading on test strips.

I've shocked it several times over the last 2 weeks, at least 13 lbs of shock in a 22,000 pool, not counting the initial shock at opening (while the pool was still very dirty). Some of those lbs were 73% "super shock" where 1 lb treats 15000 gallons.

I took a water sample to the local pool store and they found very high "combined chlorine" but almost no free chlorine, same as my test strips report. The reading on stabilizer was low but within the OK range.

Another mystery, the inline chlorinator is a "EZ-Chlor" which has a brand new canister installed. If I put a test strip in the EZ-Chlor's standing water, it shows the highest reading possible. I can see water flowing into the EZ-Chlor, and it's not overflowing, so that water must be feeding back into the pump (according to the pool place, an EZ-Chlor's outlet is supposed to feed back into the pump, unlike some inline systems). But, if I put a test strip in the pool outlet water (using a hose so only outlet water hits the strip), it still reads no free chlorine.

The best the pool place could come up with was "keep shocking it every other day". Will that work, or is there something else I can try?

[chem geek]

If the pool was "let go" over the winter, then it is possible that bacteria have converted some or all of the Cyanuric Acid (CYA) to ammonia. This will lead to a very large chlorine demand. Did you test your CYA level before closing and have you tested it now?

Be careful about using Trichlor pucks as your source of chlorine for combatting this problem. For every 10 ppm Free Chlorine (FC) added by Trichlor, it also increases Cyanuric Acid (CYA) by 6 ppm. Instead, you should shock with chlorinating liquid or 6% unscented bleach. If your Calcium Hardness (CH) is low, then you can use Cal-Hypo for shocking the pool. You don't just shock every other day. You can hit it hard every hour if you are testing FC properly.

Get yourself a good test kit, either the Taylor K-2006 you can get at a good online price here or the TF100 from tftestkits.net here with the latter kit having 36% more volume of reagents so is less expensive per test.

In addition to measuring Combined Chlorine (CC), get an ammonia test kit from a fish/pet/aquarium store. Either that, or do a bucket test to see how much chlorine will be needed before you start to get a Free Chlorine (FC) reading. 1/4 teaspoon of 6% bleach in 2 gallons is 10 ppm FC.

Richard

[CarlH]

On the water test from the pool place, the CYA level was 51 with "ideal" being 30-200. The pool has had two doses of stabilizer since opening, although I may have backwashed away the second dose too soon. Test strips consistently report stabilizer on the low side of acceptable.

Total hardness from the pool place test was low: 102 with 175-225 being ideal. Their test did not report calcium hardness specifically. Iron reading was 0, copper 0.3, manganese was "no".

I've wondered if the EZ-Chlor is working correctly because the previous owners had poked a LOT of extra holes in the canisters, presumably trying to get enough chlorine into the system, and may have been using pucks in a floater as well.

Since my earlier post, my neighbor who also has a pool and no longer uses chlorine, gave me some leftover 3" pucks, so I tossed two of them in the floater to see if anything comes of it. Since the CYA level was on the low side of acceptable, do you see a problem with that?

Thanks for the tips on test kits and I'll be visiting troublefreepool.com now...

(2 minutes later)

Hmmm, troublefreepool says that 50 ppm is the max for CYA... but pool place test says 200 is the worst, assuming they were reporting PPM. Any speculation on this discrepancy?

[chem geek]

The pool store is wrong UNLESS you use a supplemental weekly algaecide (PolyQuat 60) or a phosphate remover, both at extra cost to you and extra profit for the pool store. I suggest you buy chlorinating liquid or 6% unscented bleach to add to the pool to raise the Free Chlorine (FC) level.

[aland1905]

Using calcium hypochlorite to disinfect water is a good idea. However, rather than trying to dump some amount of pool shock chlorine into a tank and hoping that it dissolves and mixes with the water, a better idea is to mix a slurry of it in a plastic bucket (it will corrode a metal one) and pour and mix the slurry. Also, the halide (halogen, chlorine or iodine ions) need to be in contact with the water for some amount of time before they can kill all the bacteria - and that time is dependent on the temperature of the water. Colder water takes longer.

To test the degree of halogenation in water, 642-456 I suggest that people get a pool water test kit and use it. They are very inexpensive, and easy to use: Simply get a (clean) bucket of water that's been treated, and use the pool water test kit (for halogenation), ideal 'pool water' is about 2 parts per million (ppm) chlorine, drinking water should be between 2 and 5 ppm when treated - the chlorine will gas off over time, as long as the water isn't likely to be re-contaminated (in an open top tank, for example) it doesn't really need to be retreated. Dump the 'test' water out, [orthotolidine] OTO isn't too good to drink. 646-363 The test kit will have directions but basically you put the test water into a clear chamber, add a reagent--usually orthotolidine (OTO)--to the chamber, and compare the color to the provided chart. If the water tests too low, add more slurry, if too high, next time don't add so much. People will be able to figure out the approximate 'right' amount pretty quickly. 650-180 The military chlorination kits (for Lister bags and water buffalos) suggest as much as 10 ppm. This is to allow for high levels of organic material in the water (which adsorbs the chlorine, keeping it from disinfecting the water, and allowing the water to not be retreated too quickly); you probably recall drinking beverages so treated with as much fondness as I do. - Flighter