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Hot tub will not hold chlorine, even after plumbing flush


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I need help! I've stumped multiple hot tub "experts" with this problem and am driving myself crazy!

My hot tub will not hold chlorine, no matter what I do. After putting in the proper amount of chlorine and getting a proper reading (between 3-5ppm free chlorine), within one hour, the reading is back down to zero (for both free chlorine and total chlorine).

Here are details on my levels, equipment and usage:

  • Hot tub is always covered except when in use. (outdoor tub)
  • I regularly use shock, typically right after every use. I've tried both chlorine and non-chlorine shock.
  • Only 2 people (me and my husband) regularly use the hot tub, about 2 times a week. No children have ever been in the hot tub.
  • Alkalinity and pH levels are in range. (Alkalinity: 85 ppm, pH: 7.4 ppm)
  • My cyanuric acid level is in range. (94 ppm)
  • Total hardness is in range. (200 ppm)
  • Metal levels are in range. (0 ppm)
  • I've tested these levels myself using test strips AND at two different pool/spa stores that provide water analysis.

Here's what I've already tried:

  • I have done TWO spa flushes and drains with Oh Yuk Hot Tub Cleaner. I followed all the instructions and even let it sit overnight for the "stubborn contaminants" treatment found on Oh Yuk's website. After draining, I also thoroughly cleaned the shell and the cover. I also thoroughly cleaned my filter by soaking in LeisureTime Filter Clean and spraying off with a hose.
  • After draining and flushing with Oh Yuk, I attempted to switch to bromine, hoping to have better results. I had the same issue. I followed instructions exactly for bromine too. Used shock and sodium bromide to activate the bromine. Bromine levels still would be down to zero within an hour.
  • I did another drain and flush before switching back to chlorine.
  • I have tried to superchlorinate by bringing chlorine level to approximately 100pm. The levels still drop extremely quickly. With an initial reading of over 10ppm (the highest test strips go), the levels were back down to 0 within three hours.
  • Attempted to use a phosphate remover, but the level actually went higher after using the remover. I've been told by spa dealers that phosphates don't really affect water chemistry though because they are so small (parts per billion!).

Hot tub details:

  • 250 gallons
  • Water's Edge Spa, LeCirc
  • Sanitizer: Chlorine, LeisureTime Spa 56. I follow LeisureTime's instructions for the proper amount, which equals 1 tsp for a 250 gallon tub. But I've also tried using more as recommended by my hot tub dealer (approximately 3 tablespoons) but it still disappears within a couple of hours.
  • Typical temperature: 103 F
  • Purchased brand new less than one year ago (July 2020)


Does anyone have ANY ideas?! Any help would be greatly appreciated.

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  • marleecj changed the title to Hot tub will not hold chlorine, even after plumbing flush
3 hours ago, marleecj said:

My cyanuric acid level is in range. (94 ppm)

Way too high. You want 30ppm, no more than 50ppm.

3 hours ago, marleecj said:

the highest test strips go),

Strips are notoriously unreliable, get a Taylor test kit.

3 hours ago, marleecj said:

Oh Yuk Hot Tub Cleaner.

Recommend Ahhsome. Oh yuck did poorly in testing.

Do you have ozone or uv? If so, it's working. Stop trying to maintain a residual with equipment made to remove the residual.

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11 hours ago, RDspaguy said:

Way too high. You want 30ppm, no more than 50ppm.

Strips are notoriously unreliable, get a Taylor test kit.

Recommend Ahhsome. Oh yuck did poorly in testing.

Do you have ozone or uv? If so, it's working. Stop trying to maintain a residual with equipment made to remove the residual.

Thanks for your response!

  • Are you proposing that the high cyanuric acid level could be the reason why it's not holding chlorine? 
  • I did have the water tested at 2 different pool/spa stores, so it hasn't just been tested via strips.
  • I do not have ozone or UV.
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Cyanuri acid will bind to your chlorine and prevent it from working, causing you to need ever increasing amounts of chlorine to keep your water clean and sanitized.

50 minutes ago, marleecj said:

I do not have ozone or UV

Are you sure? Most new spas have ozone, and ozone eats chlorine. A good ozonator on a 24/7 injection system does exactly what you describe. It's what you want from ozone. This let's your chlorine destroy any pathogens in the water after use then be removed before your next use.

@dllenodid some tests of various purge products and found ahhsome to be the most effective by far. Not all purge products are the same, so we recommend ahhsome for biofilm removal.

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Couple of things going on. Your spa is overstabilzied so the chlorine can't kill which allows "nasties" to grow in the plumbing which further eats up any chlorine that is added very quickly, as you are seeing. The reason you had the same problem with bromine is because of the biofilm that is probably nicely entrenched in the plumbing when you switched over was doing the same thing to the bromine. From your description it sounds like you were using 2 step bromine (no bromine tabs in floater, just sodium bromide and an oxidizer).

Added to that you are using test strips which are useless for water balancing. Period! End of story. With a 250 gallon spa you don't have a lot of margin for error in water testing and balancing with a 2 bather load! (In fact there really is none.) Get a Taylor K-2006 if you are staying with chlorine and switch to the dichlor/bleach method. If you go the bromine route do 3 step bromine band get a Taylor K-2106 for bromine. There are pinned posts in the spa water chemistry section of the forum. Read them.

13 hours ago, marleecj said:

I did have the water tested at 2 different pool/spa stores, so it hasn't just been tested via strips.

How are they testing? Liquid reagents, a disc read in a machine? Do you get a computer printout? Here's a little secret. Those testing machines and computer printouts are optimized to sell you as many chemicals as possible. Not saying that all pool store testing is bad but many of the people in pool stores that are testing water really don't have a clue. Also, when balancing water (such as when lowering TA) a LOT of testing needs to be done possibly every hour or so to monitor the progress of the procedure so pool store testing just isn't practical for water balancing either. A good test kit is  the BEST investment you can make in your spa and the most important piece of equipment you can have.

 

On 6/8/2021 at 7:27 PM, marleecj said:

LeisureTime Spa 56

This is dichlor. For every 10 ppm of FC you add with dichlor you are adding 9 ppm of CYA (cyanuric acid). A tub on only dichlor quickly becomes overstabilzed, the chlorine stays bound to the CYA and is unavailable to fight the 'nasties' in the water that form biofilm, keep the water sanitized, or oxidize organic matter (Every bather introduces urine, feces and sweat, which is chemically almost identical to urine, into the tub and when you only have 250 gallon of water and 2 bathers that a lot of organic matter so the overstabilized chlorine doesn't stand a chance.)

You need to follow @RDspaguy's advice and purge, possibly more than once.

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Also, a fun fact that you are probably not aware of. High sanitizer levels can and will beach out both DPD testing with liquid or tablet/powder/disc reagents and strips that use DPD or syringaldazine for testing sanitizer leading you to believe that sanitizer levels are low or non existent when in reality they are high This is why I recommend the Taylor K-2006 and K-2106 test kits because they use the FAS-DPD test for sanitizer which does not suffer from the same problem.

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