Free Chlorine (FC) level doesn't want to go down

mbender71

Gold Supporter
Mar 15, 2021
22
Orlando, FL
Hello everyone!

This is my first post, and I want to thank *everyone* who has ever posted for the incredible wealth of information. My wife and I purchased our home 1.5 years ago that came with a pool. I elected to continue hiring the same pool maintenance service since this is my first pool, and we did a major remodel (gutting) of the home, which left me with little free time to deal with learning how to take care of a pool. Now that the remodel is complete, I'm getting into the ins & outs of pool care, repair, and upgrade of our 16-year-old pool.

Being a newbie, I went through the typical steps of stupidly purchasing test strips and then a cheap chemical test kit until I found TFP. I have since learned a lot and only follow the professional advice found here on TFP. I have thrown away my test strips and cheap chemical kit and switched to TFTestKit's TFP Pro Salt kit. I'm in heaven! I also picked up Apera's PH60 pH meter since I think the color comparison tests are complete rubbish (good luck distinguishing OT and pH with any accuracy). For the past week, I have brought my pool to proper water balance by raising alkalinity and CYA, but only to *low* levels since I'm on a mission to remove some staining that the plaster surface has. I'm preparing the pool for stain testing using Jack's Magic Stain ID kit, so the following chemical levels *will* show lower than desired levels. I am having the darndest time with lowering the FC. The pool service had kept using my SWG at 100% and using chlorine tablets which led to really high chlorine levels. I removed the tablets a week ago and, for the past three days, have had the SWG turned off to get to 1 ppm to 3 ppm FC for the Stain ID kit. It's not going well.

Current Pool Levels (from TFP Pro Salt Kit + calibrated pH meter) :
FC: 3.5
CC: 0
pH: 7.24
TA: 80
CH: 375
CYA: 55
Salt: 3800
Pool Temp Avg: 85F
Pump Run Time: 5 hours per day at 65 GPM (13k gallon pool)
Misc: North-facing pool with enclosure with no foliage to block the sun.

I've watched the FC drop about .5 ppm every two days since the SWG was turned off four days ago. It's been pretty sunny and a little rainy in the evenings. Only my wife and I go in the pool for about 1 hour a day, and we really don't splash around a lot, so FC isn't going to escape much there. I just can't figure out why the FC isn't dropping faster. It's as if there is a magical FC buffer in the pool (other than the CYA, which is at low levels). I just ordered Jack's Magic After Shock chlorine reducer in hopes of reducing my FC to 1 ppm so that I can reliably use the Stain ID kit *plus* do whatever treatment is necessary to de-stain my pool (I'm really thinking it's iron build up over the years since the eyeballs I replaced all have a brown color stain in the areas that the water isn't passing by).

Thank you very much in advance for all your help and advice!
 
Welcome to TFP.
You have done a lot and really up to date on the TFP methodology.
Overall your pool balance looks great.
We report CYA in decade numbers because the CYA tube is a logarithmic scale so not feasible to interpret between the decade lines.
I am surprised that your CYA is not higher if the pool service was using tablets along with SWCG. If the tablets were trichlor they would be adding chlorine & CYA.
Maybe you just fortunate that your FC drops slowly. Every pool is different with various UV exposures, bather loads, etc. With your CYA of 60 you are just about perfect for use with your SWCG.
Good Luck with the stains
Have you read
 
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