How high is too high when it comes to FC?

josuekm

New member
May 8, 2018
4
Northern CA
Pretty new pool owner here. I recently had to SLAM my pool to address a green algae issue. Because my CYA was/is so high (150 ppm), I had to bring my FC to about 60 ppm to kill the algae. That was about a week ago. Currently my FC is about 38 ppm (CYA about 140 ppm) and I can’t get a straight answer anywhere on whether it is safe to swim in. The CYA/FC chart doesn’t provide for my CYA level, but by extrapolation I am guessing I should be in the 18 ppm range before it is safe to swim. Am I on the right track or overly concerned and the high FC is fine for swimming because of my correspondingly high CYA? Thank you.
 

IceShadow

Gold Supporter
TFP Guide
Jun 8, 2019
2,177
Milwaukee, WI
Welcome!

FC is safe to swim in up to SLAM level, which is 40% of CYA level. If it is 140ppm of CYA, that is 56ppm FC. However, the CYA test is somewhat subjective and has a bit of margin of error and that doubles when you do the dilution method. You could easily have 120ppm or so, which means 48 is SLAM level.

At that high of CYA it’s really recommended to exchange water to bring it down. You won’t be able to test for pH with the phenol red unless your FC is below 10, which is dangerous with CYA that high.
 

setsailsoon

Gold Supporter
LifeTime Supporter
TFP Guide
Oct 25, 2015
2,993
Stuart/FL
Your pool is not safe because it's not disinfected properly. If it were me, I'd start over. Start by exchanging water so your CYA is correct first. Follow the SLAM process meticulously. Remember it's not a one-step treatment. It's a process. Then keep your water chemistry in balance. It works great this way and is dirt cheap with generic chemicals.

I hope the video below is helpful. Ask any questions, we're here to help.

Chris

 

josuekm

New member
May 8, 2018
4
Northern CA
Thank you both. I am draining as I type this reply. Unfortunately my returns are only set at about a foot below the waterline, so I will have to drain, refill, and repeat a few times. I have a pebble tech (pebble sheen) finish. I have heard there are issues with this type of finish and exposure to air once it has already been covered by water. Any feedback on this topic is helpful. Thanks.
 
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IceShadow

Gold Supporter
TFP Guide
Jun 8, 2019
2,177
Milwaukee, WI
Thank you both. I am draining as I type this reply. Unfortunately my returns are only set at about a foot below the waterline, so I will have to drain, refill, and repeat a few times. I have a pebble tech (pebble sheen) finish. I have heard there are issues with this type of finish and exposure to air once it has already been covered by water. Any feedback on this topic is helpful. Thanks.
Do the exchange Marty listed. A cheap sump pump is all you need. :)
 

josuekm

New member
May 8, 2018
4
Northern CA
Thanks, Chris. I did follow the SLAM process meticulously. My question is a different one than you are answering I think. I simply want to know if the water is safe to swim in now that the SLAM process is complete but while I still have really high (albeit below SLAM) FC levels.

Your pool is not safe because it's not disinfected properly. If it were me, I'd start over. Start by exchanging water so your CYA is correct first. Follow the SLAM process meticulously. Remember it's not a one-step treatment. It's a process. Then keep your water chemistry in balance. It works great this way and is dirt cheap with generic chemicals.

I hope the video below is helpful. Ask any questions, we're here to help.

Chris

 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
29,926
Laughlin, NV
The problem is your CYA and other parameters at those levels are very hard to test accurately. So it is really up to you. If you believe the test results you have, then swimming in the pool as long as the FC is above minimum and below SLAM level is safe.
 
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setsailsoon

Gold Supporter
LifeTime Supporter
TFP Guide
Oct 25, 2015
2,993
Stuart/FL
Sorry for the delay but no Marty said it for me. For me I want to be certain the FC level is adequate for good disinfection. If not TFP recommended levels. Of course it's a judgement that you have to make for you.

I hope this helps, and thanks Marty.

Chris