New hot tub owner and chemistry issues

JedTheHumanoid

New member
Dec 6, 2020
3
Ontario
Hi,

I have had a hot tub (brand new) for 2 months now. After filling, I had balanced the levels as recommended in the hot tub manual, and hadn't had any problems. I had filled the tub with soft water (from the tap with a water softener, since I am on a well and without this there would be too many metals/iron in the hard water), so had to raise the Calcium hardness to around 180 mg/L.

I have been regularly testing with my Taylor K-2006 kit and levels have been OK. Within the past week, however, I have noticed a slight "musty" smell on our skin after exiting the hot tub. It is barely noticeable when in the tub, but clearly something is off. I have shocked it a few times with an oxidizer shock (the manual says to never shock with Cl). The hot tub is ozonated, btw.

I tested everything today and here is what I got:

FC - 7.0 ( i had just added granular chlorine, so this is on the high range but it does tend to reduce to about 2.0 in a day's time with daily bathing)
CC - 1.5
pH - 7.9
TA - 80
CH - 280
CYA - 30
Temp - 101

This reading surprised me:

1) CC shouldn't be this high, correct? I have read that it could be influenced by shocking with oxidizing shock, which gives false CC readings. However, I last added oxidizer in 3 days ago.
2) CH is much higher than when I last tested, which was admittedly over a month ago (since I haven't been regularly testing for CH as I thought it shouldn't drift)

I need to lower the pH asap--I have been using granular pH reducer, but also have muriatic acid on hand. I have had to reduce the pH on a weekly basis as it drifts from about 7.4 to 7.8-8 in a week's time. If I reduce again, will I end up lowering the TA too much? How do I lower pH but not by TA?

Any tips on what could be causing the smell, and what I should adjust my levels to?
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
22,113
Northern NJ
Pool Size
35000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-60
Welcome to TFP.

Did you clean your new spa with Ahhsome?

Even a new spa needs to be cleaned. The pipes and equipment have oils on them and the spa is tested in the factory and water is left in them which can crate biofilms.

 
Last edited:

JedTheHumanoid

New member
Dec 6, 2020
3
Ontario
Welcome to TFP.

Did you clean your new spa with Ahhsome?

Even a new spa needs to be cleaned. The pipes and equipment have oils on them and the spa is tested int he factory and water is left in them which can crate biofilms.

Thank you. I'm sorry, I had meant to address that. No, I did not, and after reading around here a few nights ago, I realized that I should have. I have ordered some Ahhsome and am waiting for it to arrive. Hopefully that is the only problem!
 
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Newdude

Gold Supporter
TFP Guide
Jun 16, 2019
5,379
NY
Hey Jed and Welcome !! Hot tubs chemistry is inherently nasty and if you look at it that way going forward, you’ll probably keep your FC on the higher side to combat that. A regular pool can expect to lose about 4 ppm in FC a day with regular use. But there are thousands of gallons of treated water per swimmer to absorb their sweat, oils and residual shampoos/fabric detergents. In a 500 gallon hot tub with 2 people, you only get 250 gallons each, the same as having 140 people swimming in my 35k gallon pool. Imagine how quickly my pool would get cloudy and foul smelling with 140 swimmers yet 2 (or more) of you hop in the hot tub and sweat like crazy without even thinking about it. If it’s a quick soak it’s no big deal, but if you’re in there for 30 minutes, or have 4 people enjoying it, it can get funky in a only a matter of minutes. If you start a little on the high side it will buy you some time to counter balance the quick burn off of FC. Then immediately treat after to be back in range to kill any residuals. It could literally be that simple, and the ahhsome will certainly help make it even cleaner.

I had similar smells in my hot tub and couldn’t understand how I just treated it and needed more after only 45 minutes of use by myself. Now I realize that it was like having 70 people in my pool and that changes my mental equations drastically.
 

RDspaguy

In The Industry
Mar 21, 2020
1,092
Cabool, Mo
It is an Evolution Spas Rockland 27-jet, made my Strong Spas. The filter runs for 2 hours each, 2 times a day. I assume that means the ozonator runs at the same time (?) but really don't know!
I ask because ozone (and uv) will deplete chlorine levels. 4 hours per day would not account for that much loss. Many spas that have a 24 hour circulation pump also have continuous ozone. I am not familiar enough with that brand to say.
 

jseyfert3

Silver Supporter
Bronze Supporter
TFP Guide
Oct 20, 2017
1,343
Southern WI
Pool Size
15000
Surface
Vinyl
Chlorine
Liquid Chlorine
I need to lower the pH asap--I have been using granular pH reducer, but also have muriatic acid on hand. I have had to reduce the pH on a weekly basis as it drifts from about 7.4 to 7.8-8 in a week's time. If I reduce again, will I end up lowering the TA too much? How do I lower pH but not by TA?
You don’t need to lower pH ASAP, 7.9 is fine. You can wait till it reaches 8 to lower if you’d like.

You cannot lower pH without lowering TA. Going down to 50 ppm of TA is acceptable. The lower the TA, the slower the pH rise. Near a TA of 50 the pH rise is usually very slow if you let it “hang out” in the upper 7’s rather than forcing it down to the lower 7’s all the time.

I’m not sure what your fill TA is, but mine is about 325. That creates insanely fast pH rise, so I do the acid/aeration method to knock this down to around 100. Once there it’s manageable by after use acid additions, and when it reaches 7.9-8 I will knock it down to around 7.2. Then once the TA drops to around 70-80 I’ll stop dropping the pH that low and target 7.6 or so when I need to add acid.
I had filled the tub with soft water (from the tap with a water softener, since I am on a well and without this there would be too many metals/iron in the hard water), so had to raise the Calcium hardness to around 180 mg/L.
Manufacturers levels are often based on outdated information and somewhat arbitrary. Do you have a regular acrylic hot tub? Check out the TFP recommended levels (where acrylic would use the “vinyl” pool type). Note that a CH of zero is acceptable, where the only issue with no CH may be foaming. On your next fill you could try not adding CH and see how it works, then add some if you have any foaming issues.

Not sure why it jumped from 180 to 280. Did you test after adding calcium to get that 180 number? Did you allow sufficient time for it to dissolve after adding before testing?