Strong chlorine smell from new swim spa

Kletust

Member
Jun 8, 2016
11
South Carolina
Background:

My new ATV 17' Swim Spa (2400 gallons with ozonator) was delivered last Thursday. Based on flow rates I was getting from my tap I was expecting it to be full by that night, so when it was about half full I added enough dichlor to raise the final pool fill to 10 PPM FC. Unfortunately... not long after this my flow rate dropped and I had to start nursing my well and well pump along. It took until late Friday night to finish the fill, and by that time I had a pool full of tea colored water even though all of the fill water went through the in house filtration system and an inline fill filter on the hose. Initial water readings were: FC - 10, CYA - 9.2 by calculation, TA - 140, PH - 7.2, CH - 110. By this time, it was late, so I added enough Calcium to get my my CH to around the 160 mark, and then after that aerated for a while my PH was up to 8, so I added enough PH down (all I had at the time) to get PH to 7.0 and left the swim spa to do it's thing overnight.

Thankfully, when I woke the next morning I had nice clear water (Was really worried about having Iron and having to try to remove or sequester it). The swim spa was nowhere near warm enough to swim in yet, so throughout the day I slowly performed PH/Alkalinity lowering cycles and added a little more calcium to get CH up to 185. By nightfall, FC was around 8, CYA - 9.2, TA - 100, PH - 7.7, CH - 185). I now had Muriatic Acid, so I added a little of that and went to bed.

I didn't get to touch the spa Sunday, but by the time it finally warmed up to 85 that night, I had numbers of: FC - 6.5, CYA - 9.2, TA - 70, PH - 7.7, CH - 185, CC - 0. My 5 yr old and I swam for about 1.5 hours and when we got out all the numbers were the same except FC was down to 6.0. I wanted to drop the PH a little at that point, but it was in the low 40's outside, so we just ran inside and let it be until monday.

Monday Evening Numbers: FC - 2.0, CYA - 9.2, TA - 70, PH - 7.7, CH - 185. I decided at this point that PH was holding steady and by my calculations this would be a good time to add boric acid to raise borates. I added 5 lb of boric acid, which had the calculated effect of dropping PH by 2.5 ish and adding 44 ppm of borates. I let the boric acid circulate for 30 min with full swim jets, then added Dichlor to bring FC to a calculated 4PPM. About 2 hours later I went for a 45 minute swim. Post swim numbers were: FC - 4.0, PH - 7.4, TA - 65, CH - 185, CYA - 11, Borates - Between 30 and 50 per Lamotte test strips.

I give you all of that information to ask a few questions:

1. The Swim spa has had a very strong chlorine smell since it was filled. I'm assuming that this was due to high FC with very little CYA, and the swim spa has mostly been covered due to rain and extra insulation to allow the heater to heat it. I haven't tested for CC every time, but so far every test has shown zero CC. Our first swim at FC of 6.5 and CYA of 9.2 was fine. You knew the chlorine was there but it was tolerable. I did smell like chlorine after the swim though. Is this about normal? I know that my FC is a little high for my CYA level, but I guess I was more afraid of zero chlorine than too much chlorine while trying to learn the pool. Based on a very small sample size, and near continuous pump usage due to the heater... I seem to be losing about 2 PPM on days where there is no bather load and twice that when we've gone for a swim. My guess is that to minimize the chlorine smell I should aim for about 2 ppm at the time I start my swim, and then add the chlorine afterwards to make up for losses due to swimming?

2. I swam last night about 2-2.5 hrs after adding the boric acid. Maybe it wasn't a good test since it had been added so recently and the swim spa had been fully covered... it was 41 degrees and pouring rain, so when I went for my swim I literally uncovered it and jumped in. The chemical smell was super high and my skin immediately started to itch a little. My PH readings from my new Taylor kit seem to match the PH from the crappy test strips the pool company gave me so I'm guessing the post swim PH of 7.4 was right but I guess it could be off. I thought borates should make the water nicer to my skin, but it has felt dry and itchy today, and I smelled a chlorine like smell even after taking a shower after the swim. Today, I keep getting a whiff of pool chemical smell when sitting at my office, working. I definitely didn't notice the smell this bad after the first swim with no borates and higher FC.

I'm guessing my swim tonight will give me a better feel as to whether things have settled down, but I wanted to ask on here if there is anything obvious I might be missing besides trying to maintain a lower FC until I can get CYA up to 35 ish? I have some MPS shock on hand. Should I try it or not? I don't think I should need it yet, but I also found out about Ahh-some too late and didn't get to order any to do a first purge.

3. I don't think that my FC will be below 1 when I get home today but there is always a chance. If it is.... should I shock it, or should I just raise it back up to normal levels?


Thanks in advance!
 

Dirk

Gold Supporter
TFP Guide
Nov 12, 2017
4,409
Central California
Just bumping your thread. I think you've got a CYA issue. You're going to be asked how you're getting CYA values like "11" or "9.2." Not from a Taylor K-2006, surely...

:bump:
 

Kletust

Member
Jun 8, 2016
11
South Carolina
I mentioned it once, but didn't continue all the way though... so it could easily have been missed. All CYA levels so far are calculated based on Dichlor additions to fresh pool fill. Once CYA gets above 30 I'll do the actual CYA test.

So far I've added 7 oz of Dichlor to 2400 Gallons = 11.0 by PoolMath
 

Dirk

Gold Supporter
TFP Guide
Nov 12, 2017
4,409
Central California
Gotcha. It's my understanding that CYA not only protects FC from the sun, but also from the skin. I think you've got too much chlorine in the water for that level of CYA, exacerbated by the size of your pool. But I don't know anything about swim spas, so I'll defer to those that do... Hopefully they'll be along in a bit...
 

Kletust

Member
Jun 8, 2016
11
South Carolina
Just a quick followup in case anyone is trying to learn a swim spa.

I ended up solving my smell issue by super-chlorinating. I think the smell I was noticing was just chloramines from gunk that was left over from the test fill at the factory. Once I shocked the heck out of it the smell went away pretty quickly. Once I got the swimspa balanced and burned off the initial gunk its been relatively trouble free. PH is locked at 7.4-7.6 and TA is running about 50-55. I haven't done a thing to PH or TA in over a month. I lose about half of my FC each day, so I maintain FC around 6 (poolcalc calls for 3-6) in case I forget to go out and add bleach one day. I use about 12 oz of 8% bleach per day... 16-20 oz if I swim. Whenever I have the whole family (Myself, wife, and three 4-5 yr olds) I'll hit it with around 32 oz as we get out.
 

Oly

Gold Supporter
Jun 28, 2017
1,170
Fresno, CA
Yes the chlorine smell is a clue that there is a problem. The fact that this chlorine smell is commonly associated with public pools is telling.

Regarding your FC loss, you need to do an overnight free chlorine loss test. It is possible you need to SLAM your system to eradicate a low level algae situation.

Nice job dialing in your pool water chemistry and it confirms that accurate and repeatable testing at home is the foundation of a trouble free pool.