FC dropping like it's hot (in my spa)

[joshattack]

Hey all,

First, thank you for this forum. I've learned a lot! I think I'm also very confused. After having some company for the weekend, I noticed that my FC went to 0. I decided to do a SLAM to bring it back to health. Post SLAM, FC levels (once I started measuring again) went from 12 to 5 in 3 24-hour periods with no bathers. So, about 2.33 ppm/day or 0.097 ppm/hour. This was at 30ppm CYA. Today I measured the FC dropping from 7.5 to 5.5 in only 9.5 hours. So, about 0.211 ppm/hour. This was at around 40ppm CYA (which I raised with dichlor in hopes that I could reduce loss).

I've searched a bunch on the forum for the typical FC loss for a spa, but I'm unable to find it. This seems too much though, as I've read that maintenance of chlorine in a spa should only require a couple teaspoons of liquid chlorine a day. I'm going through a lot more than that.

This isn't fun anymore . Most of my interactions with the hot tub are maintaining it but rarely to go in. Please help!

Edit: Forgot to mention: the SPA looks pretty great, and smells fine.

 

[Mdragger88]

Your fc is consuming organics left behind in your tub.
You must replenish the fc that is used up during each use + enough to maintain min for your cya FC/CYA Levels until u wish to use/check on the tub again.
This could be a little or alot depending upon bather load, length of the soak, & organics present on said bathers & their suits. Obviously your tub volume plays a factor here as well along with whether or not u have uv or ozone. 2 bathers in my small tub for 45 + minutes can eat up 4-6 ppm. There’s no telling how long your fc was below min for your cya but every minute after that occurred you can bet that organics were proliferating.
I don’t know where u read that it only needs a couple teaspoons of bleach but i can assure you that method will run u into trouble quickly.
I have a small 200 gallon tub & to add 10ppm fc it takes a little over 2.5 oz of 10% bleach.
The level of cya has no effect on how well the fc lasts if it is a covered spa. That only holds true for outdoor pools & outdoor uncovered spas as cya is “sunscreen” for chlorine so it helps it last longer. In a covered spa or indoor pool the cya is there to reduce the harshness of the chlorine thereby allowing you to maintain higher levels of fc which helps keep you farther from the no no zone of zero fc.
The minimum fc level required to be effective however increases with cya level.
So Now your shock/slam fc level is 16ppm.
The key is that you never let fc go below minimum for your cya or else u will be playing catch-up with the nasties
If u are having a long fun soak with lots of people you may need to add some chlorine after an hour then continue on.
Please fill out your signature to help everyone answer your questions more specifically.
You did not list cc’s
Nor if you have ever preformed an Ahhsome purge
If you have not done one - now is a good time.
You mentioned a slam - did u raise to slam level just once or did u maintain that fc level until you have .5 or less cc’s & the clear water?
You may need to go another round two if you feel you still have a higher than normal standby fc consumption.

 

[joshattack]

Hi, thanks for your help.

I don’t know where u read that it only needs a couple teaspoons of bleach but i can assure you that method will run u into trouble quickly.
I have a small 200 gallon tub & to add 10ppm fc it takes a little over 2.5 oz of 10% bleach.

I guess I'm not seeing how these two statements are related. PoolMath has been useful for me to calculate how much LC needs to be added to achieve a certain ppm. The amount of LC I need to add to achieve that ppm is unrelated, so far as I can see, to the amount that I have to add daily for a hot tub that isn't getting used. Given the current FC consumption rate (0.211/hour or ~5/day) and my CYA level (~40), I'd have to add about 1.9oz of 10% LC daily. I'm just trying to find out if that's reasonable or not.

You did not list cc’s

I check them. They've always been under .5 after the SLAM.

Nor if you have ever preformed an Ahhsome purge

Done about a month ago.

You mentioned a slam - did u raise to slam level just once or did u maintain that fc level until you have .5 or less cc’s & the clear water?
You may need to go another round two if you feel you still have a higher than normal standby fc consumption.

I maintained that level until I had less than .5 CC, clear water, and a low FC drop. Again, post SLAM, pre-use, I averaged a daily drop of 2.33 ppm/day.

I'm still hopeful that you can give me some sense of what a reasonable daily drop is for a 290 gallon tub assuming it's not used in that 24 hour period.

Thanks!

 

[wireform]

Noone can give you this info as evey hot tub does its own thing. By learning the quirks of your hot tub management you will soon see a pattern that works. Heated water with some nasties will make it drop fast enough. Don't be so careful of the 1.9oz that you add as for now you're skirting the fence. Give it more so after the drop you're atleast above target.

 

[joshattack]

Okay, thanks. But how do you determine when it's time to SLAM. One of the doneness criterion for the OCLT is a <1ppm drop in FC (I take this to mean the 8-hour drop since the hot tub is covered). I guess I got there post-SLAM, but the drop is much more now. Do I just need to look at CC and forget the 8-hour drop?

 

[wireform]

CC on the tub is tricky when the cover is closed for so many hours and of course if you check it immediately when uncovered it'll be higher. It needs to outgas for some time before the test on the CC can be accurate.
CC is your indication of "do I need to slam". The FC loss is the nature of the beast. Learn your hot tub and be ahead of it. If you expect heavier bather load then the usual, some people ad LC in advance of getting in so the level never drops below the threshold and then as soon as they're done give it another.....to consume the fresh organics immediately.

 

[Newdude]

Hey Josh and Welcome !!!

This was at around 40ppm CYA (which I raised with dichlor in hopes that I could reduce loss).

CYA protects FC from the suns UV (loss). It’s all but irrelevant in a mostly covered tub. For that reason it isn’t needed at all, but it’s still reccomended for bather comfort as it makes the FC feel less harsh on the skin. So it helps in a tub, but not for the reason it does in an outdoor pool.

All tubs consume different amounts of daily loss. If yours is unusually high, we recommend an AhhSome purge for the plumbing. Biofilm grows like crazy there and can be the reason for the higher than normal loss. Even brand new, tubs can be nasty. They are factory tested but never fully drained/cleaned and the leftover plumbing water goes stagnant by the time you get the tub. It only gets worse from there with time.

Another huge piece of the puzzle is the person to gallon ratio. 4 people in a 500 gallon tub is the equivalent of 160 in a 20k pool. And the pool swimmers aren’t sweating away at 104 degrees having their skin exfoliated by the jets. Residual shampoos/ laundry detergents / etc come out in pools too, but not to the extent as in tubs. Certainly not as quickly either. Make no mistake, you aren’t having a nice soak with the family. You are making people soup. As such, you will need to treat it accordingly. A few PPM, per person, per half hour is expected. Over time you will see what to expect. Maybe by yourself for 2 cycles (30 mins) you lose 3 PPM. For 4 of you it will usually be 12. Once you get your baseline you have a much better idea, but it will change also. Friend A has a suit that holds more laundry residuals and\or thick hair with more leftover conditioner. It may go up today and down tomorrow. Reusing suits without washing them helped the loss once we got over the notion that what we thought was clean, really wasn’t. Fresh out of the shower and washing machine was adding more things to eat FC, even though I believed I was as clean as could be.

So adjust your thought process to think of all the things you’re adding to the tub. Sweat, body oils, exfoliated skin, detergents, half a margarita and some hot wing sauce. Treat accordingly per your testing, the tub will tell you what you need if you listen. If you know you will be having more users, start higher to help cover the loss, up to SLaM level on theFC/CYA Levels. Raise it again after to help all the residuals you left with use.

Purge with Ahhsome at your first refill to know that you are starting as sanitary as possible going forward.

 

[Newdude]

See post #50 for a Ahhsome crash course courtesy of @jseyfert3

26' Intex - Planning, Install, Upgrades, and Landscaping Thread

Preview, filling after first dump and wiping all walls with Ahh-some in a spray bottle. My hair is a bit wet as snow is falling. Supposed to get up to 6 inches tonight and tomorrow. This is a really nice spa. The dirt anf cloudy water was hiding some of that beforehand. I don't have filters in...

www.troublefreepool.com

 

[Mdragger88]

Hi, thanks for your help.


I guess I'm not seeing how these two statements are related. PoolMath has been useful for me to calculate how much LC needs to be added to achieve a certain ppm. The amount of LC I need to add to achieve that ppm is unrelated, so far as I can see, to the amount that I have to add daily for a hot tub that isn't getting used. Given the current FC consumption rate (0.211/hour or ~5/day) and my CYA level (~40), I'd have to add about 1.9oz of 10% LC daily. I'm just trying to find out if that's reasonable or not.


I check them. They've always been under .5 after the SLAM.


Done about a month ago.


I maintained that level until I had less than .5 CC, clear water, and a low FC drop. Again, post SLAM, pre-use, I averaged a daily drop of 2.33 ppm/day.

I'm still hopeful that you can give me some sense of what a reasonable daily drop is for a 290 gallon tub assuming it's not used in that 24 hour period.

Thanks!

My point above was that Generalized statements about how much a tub consumes daily are irrelevant- so long as you’re testing & doing what poolmath tells u things will be fine. Most folks here who manually dose raise their tub to slam/shock level for their cya after each use to make up for bather waste & still have enough residual fc in the water to make it to the next use/check without falling below minimum.
You seem to be keeping pretty good track of consumption now - how does this compare to consumption before? If it’s alot higher then you may want to raise it to slam again. It won’t hurt. If this doesn’t resolve the issues - a purge & refill may be in order. I doubt this is necessary by what u described especially since it was a 1 time low fc event & your water is clear.
As others mentioned the indicator for slamming a tub is persistent cc’s +.5, unclear water, or high fc consumption.
As your water ages & becomes filled with dissolved solids you will notice increased demand. Typically near the next scheduled water change/purge (@6months) I begin to notice persistent cc of .5 & a little higher demand.
Don’t over think it - just raise to slam level or close to it after using the tub if u don’t plan on using it again that day.
Be sure to leave the cover off 30 min or so to allow cc’s to escape after dosing (or adding any chems)
Also if staying on top of daily dosing is arduous for you perhaps consider a drape over swg to help w/ the base daily fc addition. Me & several others have the saltron mini that allows us to maintain the fc around the clock. Then i just supplement w/ bleach after long/heavy soaks. Or Sometimes i just hit the button
Spas/hot tubs are basically a communal bathtub in which the water isn’t changed out between uses so they are a fantastical biome that must constantly be sanitized to keep nasties to a minimum. You will always be fighting that. It can never be fully eliminated. All u can do is Stay within the safe zone (between min & slam) by using the FC/CYA Levels
As your guide.

 

[EricJ320]

I haven’t seen you mention what type of tub you have, nor does it appear to be listed in your signature. It’s worth mentioning, as I’ve learned with our new tub, if the tub has an ozone generator, that will consume the FC just as contaminants would.

Check out my recent thread where I was experiencing similar issues with FC and received some great replies from the folks here that you might find helpful.

New spa, perplexed already

Let me start off by saying I’ve been living the TFP life for about two years with our pool. I’m all in and love it, even put others on to it. The pool is dialed in, other than some brushing and dropping in MA every so often, it’s fairly, well, trouble free. So thank you all for that. Now on to...

www.troublefreepool.com

 

[joshattack]

Hey Josh and Welcome !!!

CYA protects FC from the suns UV (loss). It’s all but irrelevant in a mostly covered tub. For that reason it isn’t needed at all, but it’s still reccomended for bather comfort as it makes the FC feel less harsh on the skin. So it helps in a tub, but not for the reason it does in an outdoor pool.

All tubs consume different amounts of daily loss. If yours is unusually high, we recommend an AhhSome purge for the plumbing. Biofilm grows like crazy there and can be the reason for the higher than normal loss. Even brand new, tubs can be nasty. They are factory tested but never fully drained/cleaned and the leftover plumbing water goes stagnant by the time you get the tub. It only gets worse from there with time.

Another huge piece of the puzzle is the person to gallon ratio. 4 people in a 500 gallon tub is the equivalent of 160 in a 20k pool. And the pool swimmers aren’t sweating away at 104 degrees having their skin exfoliated by the jets. Residual shampoos/ laundry detergents / etc come out in pools too, but not to the extent as in tubs. Certainly not as quickly either. Make no mistake, you aren’t having a nice soak with the family. You are making people soup. As such, you will need to treat it accordingly. A few PPM, per person, per half hour is expected. Over time you will see what to expect. Maybe by yourself for 2 cycles (30 mins) you lose 3 PPM. For 4 of you it will usually be 12. Once you get your baseline you have a much better idea, but it will change also. Friend A has a suit that holds more laundry residuals and\or thick hair with more leftover conditioner. It may go up today and down tomorrow. Reusing suits without washing them helped the loss once we got over the notion that what we thought was clean, really wasn’t. Fresh out of the shower and washing machine was adding more things to eat FC, even though I believed I was as clean as could be.

So adjust your thought process to think of all the things you’re adding to the tub. Sweat, body oils, exfoliated skin, detergents, half a margarita and some hot wing sauce. Treat accordingly per your testing, the tub will tell you what you need if you listen. If you know you will be having more users, start higher to help cover the loss, up to SLaM level on theFC/CYA Levels. Raise it again after to help all the residuals you left with use.

Purge with Ahhsome at your first refill to know that you are starting as sanitary as possible going forward.

Mmmm, people soup. Thanks for the info and the laughs!
And, yes, I've been doing the Ahhsome purge. Should be good there anyways.

 

[joshattack]

My point above was that Generalized statements about how much a tub consumes daily are irrelevant- so long as you’re testing & doing what poolmath tells u things will be fine. Most folks here who manually dose raise their tub to slam/shock level for their cya after each use to make up for bather waste & still have enough residual fc in the water to make it to the next use/check without falling below minimum.
You seem to be keeping pretty good track of consumption now - how does this compare to consumption before? If it’s alot higher then you may want to raise it to slam again. It won’t hurt. If this doesn’t resolve the issues - a purge & refill may be in order. I doubt this is necessary by what u described especially since it was a 1 time low fc event & your water is clear.
As others mentioned the indicator for slamming a tub is persistent cc’s +.5, unclear water, or high fc consumption.
As your water ages & becomes filled with dissolved solids you will notice increased demand. Typically near the next scheduled water change/purge (@6months) I begin to notice persistent cc of .5 & a little higher demand.
Don’t over think it - just raise to slam level or close to it after using the tub if u don’t plan on using it again that day.
Be sure to leave the cover off 30 min or so to allow cc’s to escape after dosing (or adding any chems)
Also if staying on top of daily dosing is arduous for you perhaps consider a drape over swg to help w/ the base daily fc addition. Me & several others have the saltron mini that allows us to maintain the fc around the clock. Then i just supplement w/ bleach after long/heavy soaks. Or Sometimes i just hit the button
Spas/hot tubs are basically a communal bathtub in which the water isn’t changed out between uses so they are a fantastical biome that must constantly be sanitized to keep nasties to a minimum. You will always be fighting that. It can never be fully eliminated. All u can do is Stay within the safe zone (between min & slam) by using the FC/CYA Levels
As your guide.

Okay, this is making more sense. Thank you!

 

[jimmythegreek]

If your tub has an ozone system it doesn't matter how much fc you have the ozone will eat it up like candy