Spa Chemistry Clarification

[Kit]

I have a new 2,200 gallon, in-ground SWG spa. Having read much of the info in Pool School, as well as info in this subforum, I am a bit confused on optimal target levels for certain chemicals. To be specific:

From the Pool School articles, the following for SWG pools/spas have been suggested:

CH = 350 - 450 ppm
TA = 60 - 80 ppm
CYA = 70 -80 ppm.

However, in an article by Nitro in the subforum, the following have been suggested (for SWG spas?):

CH = 100 - 150 ppm
TA = 50 ppm
CYA = 20 -30 ppm.

Since the differences are substantial, I would appreciate some clarification.

Thank you kindly.

Kit

 

[pooldv]

You have a hybrid set up, sorta pool sorta hot tub, I would go with this for your set up.

CH 350
TA 50
CYA 70-80

 

[Kit]

Pooldv: Thank you. For my own information, I'm curious as to your reasoning.

Also, any additional thoughts from the experts would be appreciated. Thank you.

Kit

 

[ant 83]

Well I'm no expert, but I can give reasons that I think are relevant.

CYA slows down chlorine degradation from sunlight, so folks recommend higher CYA levels with SWG's to preserve cell life. It is thought that less chlorine burn off from sun means chlorine saved over time. Spas are usually covered, hence the lower CYA level recommendation.

TA and PH levels are correlated, and air jets in spas accelerate PH rise. Therefore lower TA levels, work better in a spa to prevent high PH. Borates are often mentioned in association with low TA in a spa to prevent PH crashes.

As for calcium, most of us have acrylic surfaces in our spas, so we don't worry about low calcium being aggressive to plaster/grout. 100ppm I believe is the low end recommended to prevent excess foaming.

I assume your spa will need to have a neutral CSI index, so your calcium/TA/PH guidelines you should follow will be determined by that.

I hope I got all that right.

 

[Donldson]

The spa recommendations are based on a fiberglass tub that is manually chlorinated and covered when not in use. As your tub is plaster you need the higher CH level and with the SWG you will want to maintain a higher CYA level. As the jets in a tub agitate the water a low TA is preferable to keep the pH from skyrocketing.

From my HTC One via Tapatalk

 

[Kit]

The spa recommendations are based on a fiberglass tub that is manually chlorinated and covered when not in use. As your tub is plaster you need the higher CH level and with the SWG you will want to maintain a higher CYA level. As the jets in a tub agitate the water a low TA is preferable to keep the pH from skyrocketing.

From my HTC One via Tapatalk

Donaldson: Does a higher CYA level apply for a SWG spa even if the spa is covered (as ant83 suggested above)? Thanks.

Kit

 

[Donldson]

That is up to you to figure out what works best for your own personal situation. If you want to start lower and see how it works for you then by all means, it is easier to raise CYA than to lower it. As pooldv said, a plaster tub that size is not especially common so it will take some experimenting on your part to find the best setup.

One thing I love about pool care: it is both an art and a science.

 

[Kit]

That is up to you to figure out what works best for your own personal situation. If you want to start lower and see how it works for you then by all means, it is easier to raise CYA than to lower it. As pooldv said, a plaster tub that size is not especially common so it will take some experimenting on your part to find the best setup.

One thing I love about pool care: it is both an art and a science.

Point well-taken. By "seeing how it works for you", are you referring to how quickly the chlorine level changes at different levels of CYA? Thanks.

 

[Donldson]

Yep, that is what I mean.

From my HTC One via Tapatalk

 

[Kit]

Excellent. Thanks.

 

[pooldv]

Everyone summed up my thoughts nicely above. You can get away with lower CYA if the tub is covered, maybe 40 or 50. The objective is to use enough CYA to have FC above minimum for your CYA before the next cycle of the SWG. But, since it is a hot tub bacteria will be more active at higher temps so you probably want to dose with bleach after each soak and let the SWG maintain your target FC level.

This article covers dosing for person hour bather loads after a soak. It also covers PH and TA.
How do I use Chlorine in my Spa (or pool)?

 

[Kit]

Thank you for your thoughts. As I find myself becoming educated on water chemistry, it is becomes increasingly obvious that within the parameters of the irrefutable relationships among pH, TA, CH, FC, etc., there is a certain amount of "wiggle room" within which each spa owner needs to fine tune his/her spa. So, having said that, at this point I plan to stick with a CYA of 70 - 80 & note the effect on FC. This all can be a bit daunting to a new spa owner. But I suspect that patience & experience will sort things out.

Kit

 

[pooldv]

Yes, you are getting the idea. Each pool and spa and situation is unique. It can be daunting at first, but as you understand and maintain your water over a period of time it gets clearer and simpler. Yes, there is plenty of wiggle room to maintain TFPC parameters that work in your particular situation so that you aren't continuously fighting your water. The most notable of these is TA and its relationship to PH. You're making good progress!

 

[Kit]

It's a lot easier to climb the learning curve with help from people who are willing to share their knowledge & experience. A sincere "thank you".

Kit

 

[pooldv]

You're welcome!