Spa Question

[MProcun]

I read through the Chlorine Chemistry instructions that Nitro posted - thank you, I've been looking for kind of information.

Our hot tub doesn't get much use; I haven't been in it for a year or more. Sad, I know.

This Thursday we are hosting a backyard party & I'm certain it will get a lot of use. I have been trying to balance the water and pulling my hair out in the process. I initially shocked the spa (treating it like the pool). FC was 20.

After FC dropped to 5, I set about adding my other chems (stabilizer, borax, acid, baking soda) to balance the water based on the Calculator. As you have probably guessed by now, pH and TA are swinging wildly out of control. One moment my pH is 6.8 with a TA of 10. I added 7oz of baking soda to get TA to the recommended 80 and aerated to raise pH only to see numbers jump tremendously: pH 8 and TA 180. So now I'm back to adding acid (4oz) and aerating to see if both will level out nicely. ??

Thus, I happened upon Nitro's excellent tutorial. I am trying my best to separate pool chemistry from spa chemistry. They seem the same yet different.

Here 's my question. I am a bit perplexed. I see in the instructions that is recommended to change out spa water completely every 3-5mos. Why do we need to change out spa water (once balanced, shocked appropriately, etc) when we don't do that for our pools? What am I missing?

So...do I need to drain my hot tub now in order for it to be deemed safe for the party on Thursday or can I continue with my goal of balancing the water since I previously shocked it this weekend? We do have a slow leak. So, water has been replaced at least partially (perhaps half the volume or more) in the past 10 days.

Thanks in advance.
Molly

 

[GuinnessPhish]

Our hot tub doesn't get much use; I haven't been in it for a year or more. Sad, I know.

Have you been maintaining the hot tub during the year with water in it? Or is it drained?

What are you using for sanitizer? Chlorine? Bromine?

 

[linen]

Here 's my question. I am a bit perplexed. I see in the instructions that is recommended to change out spa water completely every 3-5mos. Why do we need to change out spa water (once balanced, shocked appropriately, etc) when we don't do that for our pools? What am I missing?

As spa water gets "older" there is a build up of more and more "difficult/slow to oxidize" organics in much higher concentrations than a pool would. If you are not using the spa much, keeping it covered to keep out other organics, and keep a sufficient amoun to chlorine in it at all times...then you may not have to change the water as often. The best way to judge when to change the water is when your FC loss per 24 hours is greater than 50 %. By the way, in "new" water, FC should only drop less than 25%/day.

So do you need to change your water?

Well, if you allowed the chlorine level to drop too low previously i would (and also probably do the decontamination process).
I also would if the water is not clear.
Otherwise, I would check your FC drop for 24 hours and see if it is less than 50%/day.

 

[MProcun]

Have you been maintaining the hot tub during the year with water in it? Or is it drained?

What are you using for sanitizer? Chlorine? Bromine?

We do keep water in the hot tub year-round and use 6% bleach as sanitizer. Although, since we haven't been using the spa in recent years, we have only recently begun working to balance the chemistry.

As spa water gets "older" there is a build up of more and more "difficult/slow to oxidize" organics in much higher concentrations than a pool would. If you are not using the spa much, keeping it covered to keep out other organics, and keep a sufficient amoun to chlorine in it at all times...then you may not have to change the water as often. The best way to judge when to change the water is when your FC loss per 24 hours is greater than 50 %. By the way, in "new" water, FC should only drop less than 25%/day.

So do you need to change your water?

Well, if you allowed the chlorine level to drop too low previously i would (and also probably do the decontamination process).
I also would if the water is not clear.
Otherwise, I would check your FC drop for 24 hours and see if it is less than 50%/day.

Thank you!

Our water in the hot tub is clear. Loss of FC is not quite 50%. I added stabilizer today to assist with that (since that was my original assumption for the rapid loss). FC was 0 on July 13 which is when approximately 20in of water was added due to the slow leak. I do own up to the fact that we have been negligent with spa care over the past several years. We do need to decon the tub (another site I read linked in Nitro's post). My big question is if it can wait until after the party or if I need to jump on it tonight (due to the time crunch and my own learning curve of finding all this chemistry and spa care info today). My big concern is wanting people to have a good time yet not soak and become sick.

Most recent numbers (TFT100):
pH 7.3
FC 5
TA 130
CH 290
CYA 30

I added 2oz of acid to lower TA and pH and aerating. It's now time to take another reading.

 

[MProcun]

Quick addendum: if I drain and refill, should I use a scale preventive (like, Leisure Time Defender) since my CH is so high? We do have scale and although I realize that is a precipitate formed from the TA and pH being too high - is it recommended to also use a preventive when the CH is naturally high (290)?
Thanks,
Molly

 

[chem geek]

If you get the TA down to 50 ppm instead of 80 ppm or higher, then when using bleach there should be better pH stability, especially with the 50 ppm Borates. There is a lot of aeration in a spa. Nitro's writeup needs to be updated to say the TA target is 50 ppm and the use of 50 ppm borates (boric acid) is not optional.

With the lower TA, I think your CH will be OK and you won't need to add a stain preventer. On the other hand, if you think you won't be able to keep the pH in a reasonable range, you can always add some of the scale preventer as insurance. Up to you. The target CH is 150 ppm to prevent foaming, but with the TA at 50 ppm (assuming a CYA of around 30-40 ppm) and using 50 ppm borates, a CH of 300 ppm will not be too high.

As far as safety for the soakers, they should be fine if you start out with FC at the start of the soak. The balance will be between how much of the chloramines they are willing to smell -- if you start off with a higher FC before they get in, then it will last longer, but it will smell more as it combines with ammonia in their sweat (and urine). If they will only be in the tub for an hour or so, then bacteria won't get a chance to multiply and grow significantly. If you are concerned with person-to-person transmission of disease, however, then you'd need an FC reading in the spa at all times during the soak.

 

[MProcun]

Thank you for clarifying about the use of borate and target of TA at 50ppm.

I drained the tub last night, just to be on the safe side.

Fresh refill numbers are:
FC 0
pH 7.2
TA 330
CH 240
CYA 0

It looks like a mess to me. Your info letting me know that it doesn't matter how high my CH is was helpful - especially after seeing how high my CH naturally is.
I am more concerned about the naturally low pH and extremely high TA since the preferred (maybe only?) method for correction is acid/aeration and I am already at the threshold to aerate (7.0-7.2). I read somewhere on here that to lower the pH more risks damaging my metal equipment (pipe fittings, heater, pump).

The chems I added an hour ago according to Nitro's article and Pool Calculator (on a 500gal tub) were:
4oz 6% bleach (goal of 5ppm)
2lbs Borax (goal of 50ppm)
2C 2oz 20 Baume (to offset the borax and to lower pH to 7.0 and lower TA - then aerate to raise pH)
2oz Stabilizer (put in a sock and thrown into the filter compartment)
4oz "Defender" scale preventive...just in case. Sorry.

I currently have the jets on but no air - just to mix everything around.

Does it sound like I'm on the right track? I'm just really nervous about the pH/TA starting out so...well...bad, really.
Thanks,
Molly

 

[linen]

There was no need to add the Borax to start. That just raised your ph and TA which you then dropped back down with Muriatic Acid. But it doesn't hurt anything. I would have just started aerating with fill water already low in ph.

Now aerate the water until the ph is close to 7.8, then drop it back down to 7.2 and repeat to slowly lower your ta. Using the air in the jets will help speed up the process a lot.

 

[chem geek]

It's not that CH doesn't matter at all, but your CH level isn't too high if everything else is in balance. It's too bad your fill water TA is apparently very high, but at least with a spa it's not too difficult to get it lowered since you can significantly aerate the spa with jets.

 

[MProcun]

I was under the impression that 50ppm of Borate was a "must have" to act as an additional buffer due to all the aeration the hot tub gets. No? That's why I added it up front.

Thank you for the "cycle" tip (raising pH and lowering w/ acid, aerate and repeat several iterations) to get my TA where it needs to be. I guess I'm learning this is not a one-step process. Right? My error.

The pool, on the other hand seems to be more "one step" ish.

Molly

 

[linen]

I was under the impression that 50ppm of Borate was a "must have" to act as an additional buffer due to all the aeration the hot tub gets. No? That's why I added it up front.

I need to read more carefully (I thought you were just adjusting ph with borax ...sorry about that...what I should have said is to lower TA first and then add the Borates (if you want them). If you do it the way you did, it will take more aeration/acid cycles to get your TA down. Luckily, lowering TA is easy in a spa with jets so you should be okay.

Borates even in a spa/hot tub are not required, but they can help if you are having issues and need more ph buffer.

 

[MProcun]

...lower TA first and then add the Borates (if you want them). If you do it the way you did, it will take more aeration/acid cycles to get your TA down. Luckily, lowering TA is easy in a spa with jets so you should be okay.

Ah-ha! That makes total sense (I am learning, slowly but surely) - thank you!

Can I aerate for an hour and re-check or is that too long/too short (as a general rule) between acid/aeration cycles to get an accurate test result?

Molly

 

[linen]

An hour interval is fine to start when doing aeration in a spa since it is quite effective. Once you see how fast the ph goes up you can adjust your testing interval.

 

[MProcun]

Awesome, thanks so much!

 

[chem geek]

The outgassing is faster at lower pH so if you check on the spa and see that the pH has risen some, but not to 7.8, you can still add acid to keep it lower. The fastest would be keeping it in between 7.0 and 7.2 but when the TA is high it should not take very long for the pH to rise that much, BUT with the 50 ppm Borates it does take longer (that's why you use them, though usually after the lowering TA procedure).

 

[MProcun]

I don't know how fast or slow this process was overall.

I retested the spa about 2hrs after the initial chem were added and got these results:
FC 1
pH 7.3
TA 250
CYA 20

I then added 4oz of bleach for a goal of 5ppm and 1C of acid to continue to lower TA and put my jets on full bore. I did not add any more CYA - there was still some left in the sock inside the filter compartment.

I retested an hour later:
FC 5
pH 7.8
TA 160

I added 1C of acid and continued to aerate full blast.
I retested an hour later:
FC 5
pH 7.5
TA 80
CSI 0.02

I'm a bit nervous about a TA of 80 when 50 is considered to be ideal but the CSI indicated "balanced" so, I put the cover back on and will test again in the morning. I will have all day to adjust/tweak before guests arrive in the evening. Was this the right thing to do?

So...3hrs to adjust the TA. That didn't feel slow to me.

I thought I could definitely see the borates working to keep pH maintained. I'm guessing that otherwise I would have seen major shifts in pH (and maybe in my naivete been tempted to add more acid than necessary to get the TA down ?). I felt like borates may have helped to allow the TA to have a controlled drop. Is that correct?

Thanks for walking me through this - we have 20 excited ladies coming to swim tomorrow night!
Molly

 

[chem geek]

1 cup of dry acid should have lowered the TA from 160 to around 60 ppm, but if it's 80 ppm I'd add 1/4 cup more (if you're still at 80 ppm in the morning) since you really do want it a bit lower at 50 ppm so that the pH will be more stable. Great job so far! It didn't take so long because you did the process perfectly well and you also started from a rather high TA -- it's faster to get the TA lower when it's high then when it's already lower. Also, you've probably got a lot of aeration.

I presume you won't be having all 20 in the spa at once since it probably only holds around 8 or so, right? Don't freak out with how much chlorine you'll need to add after people get out of the spa -- every person-hour of soaking in a hot (104ºF) spa needs around 7 ppm FC in 350 gallons (less in higher volume; more in smaller volume; the actual chlorine amount is constant at 5 fluid ounces of 6% bleach or 3-1/2 fluid ounces of 8.25% bleach). If y'all are going to do the soaking within an hour or two, then you can add the additional chlorine after everyone has used the spa. If you are going in and out over a longer period of time, you should check the chlorine every hour and add more so you measure at least some FC residual. This will minimize chloramine smell. If, on the other hand, you think someone is coming to the party with an illness and want to be as conservative as possible, then you can treat the spa similar to a commercial/public spa and maintain the FC level at all times, but that won't be as pleasant.

 

[MProcun]

1 cup of dry acid should have lowered the TA from 160 to around 60 ppm, but if it's 80 ppm I'd add 1/4 cup more (if you're still at 80 ppm in the morning) since you really do want it a bit lower at 50 ppm so that the pH will be more stable.

My numbers this morning:
pH 7.5
FC 4
TA 90
CYA 30

I'll add the 1/4C acid as you suggest. It's not dry acid, it's muriatic 20 baume - I don't know if that makes a difference in the amt. I would like to see that TA come down to 50. I was surprised that a cup of acid didn't lower the TA by 100 - as Nitro's article indicated. So, I'll try the 1/4C to see if that gets me close & retest.

Thanks for the advice about chlorine. I'm planning to raise the FC in both the pool and the spa this afternoon a few hours before guests arrive. I recall reading on here that it should be at "near shock" levels in the pool prior to a party and I was going to do the same with the hot tub. Should my goal be 10ppm of FC in both or higher since the Calculator shows 13ppm as shock level?

I think our hot tub is meant to hold 6 people comfortably (5x5 and 560gal). That's not to say more won't cram themselves in - or hey, a fun group photo with all 20 (not sure that sounds like fun to me). I can keep an eye on the FC level depending on how popular the spa is; we are also offering our pool and the fire pit tonight (s'mores, anyone?).

Thanks for all your instruction & help!
Molly

 

[MProcun]

I got there!

Most recent set of numbers:
pH 7.4
FC 5
TA 50
CSI -0.33

Woohoo!

Would really like the CSI to say "balanced" instead of "potential to become corrosive to plaster" - but that is the old perfectionist in me, besides, the spa is vinyl not plaster.
Molly

 

[chem geek]

Yes, the volume of Muriatic Acid is similar to that of dry acid so you were fine (as you saw).

You do not need the CSI to be balanced for a vinyl liner pool/spa or for an acrylic spa. The CSI balance is only needed to protect plaster surfaces (and somewhat for some fiberglass with a calcium carbonate gelcoat). A negative CSI is desirable in a spa since there is a great tendency for the pH to rise which would have the CSI rise and could lead to scaling (we've seen that with a CSI of just +0.3 at hot temperatures -- for pools which are at lower temps scaling usually isn't seen until the CSI gets to at least +0.7).

You're good to go!