Newbie just beginning to understand "free" and "total" chlorine. . .

[Hainsworth]

Hi all! I have a 21,000 gal inground, vinyl lined SWCG pool built last year (now in second season). All is going fairly well, but on my last trip to pool store, water test showed there was some combined chlorine (which they called "chlorine lock" - uh oh . . . ), and water was ever so slightly greenish - they prescribed "shock" a "non-chlorine" product that had an active ingredient of potassium monopersulfate (and was 55% "other ingredients" - yikes! what DID I put in my pool?) That seemed to clear it up for about 10 days, now slightly greenish again. My browsing on this site/forum has raised a red flag about blindly following their instructions.

We began the year with a failure of the salt sensor in the SWCG cell and had the unit replaced, so our chlorine was a bit low at the last test, and our salt is a bit high because the faulty unit kept saying to add more! The most recent water test results (6-1-12) follow:
FC .8
TC 1.1
pH 7.9
Hardness 234 ppm
Alkilinity 86 ppm
CA 40 ppm
Nitrate 26 ppm
Salt 4000 ppm

We fired up the new SWCG cell, lowered pH some and shocked and, as I said above, it was crystal clear for about a week. Current readings by my drop test about 3 ppm TC and 7.6 pH. Any advice anyone has on 1) combined chlorine and the best way to get rid of it; 2) recommendations for a reliable FC and TC test meters - digital - something that will give me a number not make me play "identify this shade of yellow"; or 3) causes of slightly greenish (but definately not cloudy and no sign of algae) water would be greatly appreciated.

Thank you!!

[aylad]

Combined chlorine is chlorine that is actively engaged in oxidizing goo from your water. The best remedy for it is ...more chlorine! It just means that the chlorine is doing its job. Usually if you have CC more than .5 ppm, we suggest shocking the pool until that CC level drops to zero. If it's less than .5, as in your case, just keep your chlorine levels where they need to be, keep the pool uncovered, and they'll take care of themselves. (By the way, there's no such thing as "chlorine lock", and the non-chlorine product they sold you was a really expensive way to do what you could have done with plain, generic bleach).

The FC and TC tests that we recommend are the DPD-FAS test kit (K-2006).(See the test kit link in my sig). It uses a scoop of powder to turn your sample pink, then you add drops of the reagent until it goes clear. No comparing yellows.... the complete kit is the K-2006, but if you have a drop-based kit already, the K-1515 is the standalone chlorine part of the kit. You can get them at a good price online using the Amazon link in my sig.

One of the main caues of slightly greenish but not cloudy water is the presence of metals. What is your source of fill water, and is there any known copper or iron in the water? Have you used anything containing copper (algaecides, trichlor tabs, any other type of "dual action" product) that contains copper?
!

[Hainsworth]

Thanks for the speedy reply! Interesting that you mention metal. I left it out of my original post, but the last water test said 0ppm copper and .31 ppm iron. The pool store considers the limit for irom to be .30, so they gave me a "metal out" product which I used. Our fill water source is our well, which is generally good (has been professionally tested for every contaminant known to man, as well as minerals and metals), but occasionally contains a little iron (seasonally depaning on groundwater levels and was <.03 ppm for Iron in January of 2012). Also, water gets to pool through hose on frost free hydrant which has some parts that could leach. My husband just added water (for the first time this year) today with that hose! Could the addition of new water w/ metals be reacting to earlier administration of "metal out" product? Maybe I should just let the pump go and see what we've got in 24hrs?

I will plan on getting the chlorine test you recommend and shock with bleach. Does it matter what bleach you use - obivously not the funny ones with added lavender scent, etc - but is there really any difference between the "splash-less" and all the other permutations out there these days and regular old bleach? I don't want to add anything that might cause any problem with the SWCG cell.

Thanks again.

[waterbear]

I will plan on getting the chlorine test you recommend and shock with bleach. Does it matter what bleach you use - obivously not the funny ones with added lavender scent, etc - but is there really any difference between the "splash-less" and all the other permutations out there these days and regular old bleach? I don't want to add anything that might cause any problem with the SWCG cell.

Yes, there is!!! You want plain unscented, un-splashless chlorine bleach! All the others have additives that can cause foaming or worse and are not considered to be sanitizers.

What make of SWCG do you have. CYA of 40 ppm seems on the low end and it is a good rule of thumb to run the CYA at the manufacturers high end which is usually 75 to 100 ppm depending on the make.

[Hainsworth]

Thanks Waterbear!

That's what I thought about the bleach, but I want to make sure I ask all the questions (even dumb ones ) so that I get this right! My SWCG is a Pentair Intellichlor Model IC 40. I checked the manual and it does say that optimum CYA levels for the unit are 50-80 ppm. Why should I aim for the manufacturer's high end? I appreciate the education.

[aylad]

Having the CYA at the high end of the manufacturer's recommendation will help the cell last longer.

Oh--and there are not dumb questions, when it comes to pool care!