What's up with FC reading?

[DonR]

Greetings,

I have had a new HotSpring spa (325 gallons) for a little over two months now. The new spa replaced an old spa that I had for about 15 years. When I got the new spa I purchased a Taylor K-2006C test kit, because my old Taylor K-2006 test kit was running low on several reagents. I also purchased the Taylor Deox reagent (R-0867) so that I can accurately measure combined chlorine and MPS.

The new HotSpring spa has no bypass filtration and continuous circulation, with an ozonator that (I think) operates 24 hours per day - at least there are always bubbles produced - whether the corona discharge tube is on constantly I am not sure. It also came with a silver ion cartridge, and HotSpring is now recommending the low chlorine regime with these spas, utilizing a weekly chlorine shock (dichlor) and daily MPS additions. I use the spa daily when it's not raining, and I am often the only person in it. I test the water at least twice a week and adjust the parameters as needed. Adjustments and the weekly 10 ppm chlorine shock usually occur on Saturdays. Here are the test results from today:

Temp - 101F
pH - 7.8
Alkalinity - 70 ppm
Hardness - 150 ppm
TDS - 1470 ppm (442 scale)
FC - 2.2
CC - 1.4
MPS - 10.6
CYA - 100

All of these test results are believable and in line with prior results, except for the FC, CC and MPS values, all of which are unexpectedly high. I last added dichlor 4 days ago, and the FC / CC levels yesterday were 0.2 ppm and 0.4 ppm respectively. I added 2 tablespoons of MPS last night after using the spa for about 30 minutes. After the spa water circulated overnight, I expected the MPS level to be around 4 to 6 ppm, and I expected the FC and CC readings to be very low if not undetected.

I used my old K-2006 kit to repeat the FC and CC tests, and the results were confirmed. I used a BioGuard test strip, which indicated no FC. The water is now and has always been crystal clear, with no odor of chlorine or chloramines.

Can anyone suggest what's going on with the chlorine tests today?

Thanks,

Don

 

[PoolGate]

OI.... Read the section on temporary pools.

Pool School - Guide for Seasonal/Temporary Pools

I suggest you read, empty, refill, and follow this sites guidance for pool maintenance.

 

[DonR]

OI.... Read the section on temporary pools. <br>
<br>
<a href="https://www.troublefreepool.com/content/155-guide-for-seasonal-temporary-pools" target="_blank">Pool School - Guide for Seasonal/Temporary Pools</a><br>
<br>
I suggest you read, empty, refill, and follow this sites guidance for pool maintenance.

Thanks for the reply PoolGate. I will be draining and refilling soon. I know my TDS is near the upper limit, and CYA is too high.

I am sold on the EPA sanctioned low chlorine regime that HotSpring now recommends, so I won't be switching back to the normal chlorine regime. After refilling, I will be using bleach as the weekly shock treatment, after establishing a 20 ppm CYA residual, and I will be using a borate buffer instead of carbonate.

After 15 years I am pretty comfortable with water maintenance and testing. After an initial debacle with biguanide (recommended by the manufacturer of my first spa), there have been no water quality issues in 15 years. Other than the high TDS and CYA, there are currently no water quality issues either, but the erroneous high chlorine readings have me puzzled. I'm just hoping someone has an explanation for them.

Thanks,
Don

 

[Griswald]

You can either use the "EPA sanctioned low chlorine regime" or TFP...but not both.

TFP believes in the CYA to chlorine ratio system, not in a single number.

 

[DonR]

You can either use the "EPA sanctioned low chlorine regime" or TFP...but not both.

TFP believes in the CYA to chlorine ratio system, not in a single number.

I understand and acknowledge that the CYA to chlorine ratio is very important, IF you are using chlorine as a sanitizer, and that the CYA to chlorine ratio also affects the ability of chlorine to oxidize contaminants in the water. Are you suggesting that I cannot use this website if I don't use chlorine as the sanitizer in my spa?

Yesterday I started to do an MPS test with my Taylor kit. The first step is adding a scoop of DPD. If there is no free chlorine in the water, which I expected, not having adding any dichlor in four days, there will be no pink color when DPD is added to the sample. I was surprised to see a strong pink color after the DPD was added, so I proceeded to test FC and CC. I did not believe the results, so I repeated the test with another DPD/FAS kit, which appeared to confirm the results, and then I used a test strip employing syringaldazine that indicated no free chlorine.

I posted here hoping that someone could explain these results. So far, no dice.

BTW, I did not use the spa yesterday due to weather and did not add any chemicals. The cover remained on the spa all day and night. This morning free chlorine measures 1.4 ppm and combined chlorine measures 0.4 ppm with the Taylor K-2006C kit. The test strip still indicates no FC.

 

[PoolGate]

Are you adding bleach (aka chlorine) now or are you planning on doing this as a "shock" treatment?

How did you test your CYA? Your high CYA level led me to believe you have been using chlorine tablets. Typically a very high CYA level is due to that.

Most people on this site do not need to ever shock their pool/spas. "Shocking" is not part of the TFP method. I have never had to the entire time I have owned my pool. "Shocking" is usually needed because not enough sanitizer is being used or the sanitizer is ineffective due to high CYA levels.

In response to your other question, you are welcome to come to this site for advice even if you are not going to follow the recommended site sanitizing methods. This site has no skin in the game commercially as you can see there are no ads it is entirely member supported. The "TFP" or "Trouble Free Pool" method is what we push as it has been proven to be very effective at sanitizing pools and spas with less mess, trouble and expense then other methods with verifiable better results. Certainly it is not the only method but I am not aware of anyone that practices it that has decided to revert back to another method.

 

[DonR]

Hi PoolGate,

Thanks again for your reply. I test CYA using the Taylor K-2006C kit. It has been rising predictably based on the amount of dichlor granules I have been adding.

For the first couple of weeks with this new spa I used dichlor, which of course also raises the CYA level. Then I got an email from the spa manufacturer suggesting that I should try the low chlorine regime, which relies on a silver ion cartridge similar to the Nature2 cartridge (included with the spa), ozone (generator built in to the spa) and either a low dose of chlorine or MPS after each soak. I was a little skeptical, since the last time I looked into it years ago, the mineral sanitizer method, though some people were claiming good results, was not EPA approved. I discovered that now it is EPA approved, so I decided to try it. The manufacturer's literature also stated that a "shock" level of dichlor was needed to initially activate the silver ion cartridge, and that if MPS is used as a daily oxidizer, a "shock" level of dichlor was recommended weekly in addition. I can say that the results after about 10 weeks have been excellent, with zero apparent water quality issues, and a very pleasant, crystal clear and odor free water quality. The only drawbacks I can see are:

1. There is not a reasonable way to routinely test the silver ion and ozone levels at home
2. Prolonged use of dichlor causes elevated CYA levels
3. Adding the recommended amount of MPS after each soak (about 1 ounce in my spa's volume) is a little more expensive than using dichlor would be, and causes TDS to rise more rapidly.

Despite these drawbacks, I intend to continue this low chlorine regime. I will replace the silver ion cartridge at the manufacturer's recommended 4 month intervals, and after I drain and refill the spa I will establish a CYA buffer using dichlor, then switch to bleach for the weekly chlorine additions. And when I first lift the cover, I can definitely smell the slightly sweet odor of ozone, so I know the ozonator is still working.

Of course if I begin having water quality issues in the future, I will re-evaluate my decision. So far I am very pleased. I test water parameters twice a week typically, and this week was the first time I have seen test results that defied my understanding. I'm not really concerned, but by my nature I prefer to understand the reason.

Thanks,

Don