rmcderm313 Posted January 18, 2021 Report Share Posted January 18, 2021 Hi All, I have what I hope to be a simple question. What is the maximum ppm of free chlorine in a spa to safely use it? My K-2006 test kit booklet suggests 5.0 as the max, but I'd just like to hear from the board to see if there are any caveats or further considerations. I'm using the bleach/dichlor approach, and have read all of the stickys carefully. I just haven't seen an answer to this yet. I want to make sure I'm timing my chlorine additions correctly so we'll be able to use the spa when we want. I'm on a fresh fill, 700 gallon spa. CH=130, pH=7.6, TA=50. My first Dichlor addition bumped FC to 13.5 ppm (not sure why I only used 1.7 oz which should have bumped to 10 ppm). 24 hours later it was at 10 ppm, so chlorine demand is 25%. Combined chlorine was not present, or only the slightest hint of pink. Can someone suggest or confirm the optimal FC ppm to target for when we want to use the spa? Thanks, Rob Quote Link to comment Share on other sites More sharing options...
RDspaguy Posted January 18, 2021 Report Share Posted January 18, 2021 The health department will close a pool at 10ppm. @waterbear, care to explain fc/cya relationship? Quote Link to comment Share on other sites More sharing options...
waterbear Posted January 19, 2021 Report Share Posted January 19, 2021 12 hours ago, RDspaguy said: The health department will close a pool at 10ppm. Depends on what state. For example, Alaska does not permit the use of CYA or chlorinated isocyanurates and determines required FC level by pH. They also top out at 5 ppm FC. Wyoming is interesting. They max out at 8 ppm or whatever the product label states is the maximum. They also allow a CYA level of 0 to 100 ppm without any adjustments to FC level. Bottom line, 2 ppm FC in a tub with no CYA is actually more aggressive than 12 ppm FC with 80 ppm CYA 1 Quote Link to comment Share on other sites More sharing options...
rmcderm313 Posted January 19, 2021 Author Report Share Posted January 19, 2021 5 hours ago, waterbear said: Bottom line, 2 ppm FC in a tub with no CYA is actually more aggressive than 12 ppm FC with 80 ppm CYA Thank you both. I knew CYA 'softened' the effect of FC but I had no idea it could be so pronounced. I should have about 20ppm CYA before the weekend, and will be stopping the dichlor and switching to bleach when I project to hit 30 as advised. I must admit I'm still confused about a safe level of free chlorine. If I get to 30ppm CYA, it sounds like from your statement above that I should be ok with any FC up to 10ppm (I'm just making an estimate based on the numbers above and picking a guideline FC number). I appreciate the answers and assistance. Rob Quote Link to comment Share on other sites More sharing options...
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