Soaking at low/minimum FC level?

[irekz]

Hi everyone.
Over time we found that my wife's skin is susceptible to drying/itching if I stick to "target" values suggested by TFP as we soak.

My tub has 30ppm of CYA so:
- miniumum is 2ppm FC
- target: 4-6

She is much better if we start the soak at 2-3 ppm (rather than 4-6 target), even if this means going close to zero after 1h. If we stay longer than 1h I will add extra 2ppm of bleach. To compensate this low FC - I add more chlorine after getting out (to around 10ppm), and we don't use the tub the following day (1 day of use, 1 day off). Before next soak I make sure that CC is low (0.5 or less) and FC not above 3. If FC is too high I run UV lamp for few hours.

This seems to work OK - but below TFC target, is it safe?
I wonder what are your thoughts or personal experiences.

Kind reagrds!
Irek

 

[wireform]

Yes 2 ppm is safe but gives you "0" buffer. But you have it figured out after the tub gets used and that's not to say it won't ever slip out ahead of you.

 

[irekz]

Yes 2 ppm is safe but gives you "0" buffer. But you have it figured out after the tub gets used and that's not to say it won't ever slip out ahead of you.

Thanks - your comment is appreciated.

 

[RDspaguy]

I think you are overthinking it. My fc is typically nearly 0 at use, thanks to ozone, and I treat after use. Is there some theoretical risk? Sure. But my family has never had an issue in the 12 or so years I have done this.

 

[Dirk]

Just a thought... (and I'm not a spa guy by any stretch) I'm not sure you're accomplishing anything of value by going to FC 10 after the soak, except wasting chlorine and making the spa unusable for the wife. Have you ever tried dosing the water back to just normal FC and monitoring that the next day? Then topping off to normal FC again if necessary. You should then be able to use the tub every day. My guess is, the amount of chlorine you're using to goose the spa's FC after use gets burned off more than it attacks anything.

Target level is designed to keep your water safe for normal exposure to organics. You're performing mini SLAMs every use. And SLAM level FC is designed to combat the presence of excessive organics (namely algae), which aren't really present in your water. Just as your water is safe at minimum FC (or even below for brief stints, as @RDspaguy points out), it's also safe just maintaining your target FC, rather than going to FC 10.

 

[irekz]

Just a thought... (and I'm not a spa guy by any stretch) I'm not sure you're accomplishing anything of value by going to FC 10 after the soak, except wasting chlorine and making the spa unusable for the wife. Have you ever tried dosing the water back to just normal FC and monitoring that the next day?

Going to FC10 was trying to be on a "safe" side as I am allowing water to drop below minimum for a short while. Judging from your comments this is missguided.

Just as your water is safe at minimum FC (or even below for brief stints, as @RDspaguy points out), it's also safe just maintaining your target FC, rather than going to FC 10.

That's really reassuring and exactly what I was hoping to hear - thank you.
Will try to avoid those "mini slams", this sould make easier to mantain FC level my wife tolerates well.

 

[irekz]

I think you are overthinking it. My fc is typically nearly 0 at use, thanks to ozone, and I treat after use. Is there some theoretical risk? Sure. But my family has never had an issue in the 12 or so years I have done this.

What is your starting FC - are you aiming for minium or target based on CYA?
Good to know that dropping to near zero for a short while is not a cardinal sin I thought it is!
Thanks!

 

[Dirk]

In a spa, within the short span of typical use, the water is probably only subjected to what comes off the bodies involved. That's primarily sweat, though I'll leave it to you to figure out what other unpleasantries that might include. So when you go from your starting FC of 2 down to zero, that's the stuff the chlorine has been working on. Not algae or dead animals or low-flying bird poop, etc. After use, you only need to add what chlorine is needed to finish the job, and then get you through to the next spa session. That should then become your target level, whether that matches TFP guidelines or not (as long as it's above minimum recommended FC). That should be considerably less than 10. So experiment. It'll vary, of course, especially based on number of spa users and how "clean" they are, but I bet you can find an amount of chlorine that will ride it out through 23 hours to have your tub ready for you, at FC 2 or 3, by "spa time" the next day...

If you continue to experiment, and keep track, you'll get a feel for how much chlorine to add after each session: X amount for 1 hour of two people, Y amount for 2 hours of three people, etc. It won't be an exact science, but pool and spa care is more along the lines of "close enough is close enough."

 

[RDspaguy]

Better too much than too little. The uv is going to burn off excess, maybe not as fast as ozone maybe faster, I am not sure, but overnight should wipe out most of what isn't combined by organic contaminants, as well as the cc that results from sanitation.
As @Dirk says, it's not a precise science, and it will be a little different for each circumstance. There is no set amount of fc usage per person per hour, just a ballpark, and since every tub is a different volume, that changes how much is needed to establish a certain ppm. Err on the side of caution and let the uv handle the rest.