Free Chlorine vs. Total Chlorine adjusting

[PoolDoc]

Using a drop based
kit, just opened pool last Saturday. Clean and vacuum and started filter everything working well.
Use pucks, put (4) in skimmer to start pool, but since reading here will probably change. Pool looks fair
today a bit cloudy but moving to blue. My chlorine readings are off
and I don't know how to get them satisfactory. Big difference from FC to TC. Here are my readings any suggestions appreciated.

FC 1.
TC 6.
PH 7.2
TA 100
Hardness 100

Since you say your pool looks fair and only a little cloudy, I expect that maybe your results are just inaccurate. If you truly had a CC reading of 5, then I think you would be looking at a swamp. Retest your chlorine levels again.

Actually, Watermom, those readings are pretty typical for a pool freshly opened with a biofilm in place (note the cloudy water now clearing). What would be determinative, would be to find out what Truckman's CYA readings were last fall compared to now. I'll bet he has little or no CYA now, compared to moderate or high CYA when he closed. The fact that he feeds pucks (trichlor) makes this even more likely.

What happens, is that the bacteria in the biofilm 'eat' CYA and 'poop' ammonia and urea. As soon as chlorine is added, you end up with massive CC levels. The solution is to use borax to push the pH to around 7.8, which favors the formation of monochloramine, which is the least irritating chloramine, and which also happens to be highly effective against algae and biofilms*. Then, while maintaining the pH, dose nightly with bleach, till the CC levels drop below 1.0. Continuing 'shocking' for at least a week longer, repeating doses anytime the chlorine drops below 5 ppm. This is necessary to remove any remaining urea. Unlike ammonia, it does not react instantly with chlorine.

Obviously, on some pools, you may risk calcium carbonate cloud formation, but not on this pool. And even on those, if they have a good filter (ie, not an AG sand filter!), they'll be working on the ammonia/urea mess long enough for the calcium carbonate to filter out before it becomes a problem.

Hope this helps,

Ben
"PoolDoc"

*Interestingly, because of the monochloramine, pools which open with high ammonia AND high pH will often clear almost instantly upon addition of the chlorine. But, they may show ZERO chlorine, unless the owner tests with OTO, or runs the DPD combined test. Test strips often are 'free chlorine' only, and will show zero as well.