FC reading jets on vs jets off

[Fryeday]

We have a 21,500 gallon pool and have been using this site for a year. Best looking pool ever since switching to chlorine. We bought a hot tub and have had it running about a month.

I use the K-2006 kit. Since I already use KemTech 10% chlorine for the pool, its easy to use that for hot tub too. My issue is that if my jets are on, I get a FC reading of 7 FC. If my jets are off, I get a 1 FC reading in the same exact water. What gives?

 

[ajw22]

Welcome to TFP.

@JoyfulNoise any ideas?

 

[JoyfulNoise]

It would be best not to engage in conjecture without a complete set of test results. Please post your full set of test results with the jets off and the jets on. Take a water sample from the same place in the tub, preferably the middle and arm deep, basically as far away from any jet as you can possible go. Do not skim water off the surface. Also please list all of the chemicals you are adding to your tub and with what frequency.

 

[Fryeday]

Sorry for the delayed response. Essential staff so working crazy hours right now.

Mira Reserve 600L - 350 gallons - Outdoors, but covered when not in use
Brand New Taylor K-2006 Test Kit (replaced every year)

I always take the sample elbow deep away from the jets using upside down bottle, then tilt to fill, then upside down to pull out.
10% Chlorine - It seems that I am having to add about 2-3oz every day which seems high to me? We have 2-3 bathers in the hot tub for about 30 minutes daily.
Muriatic Acid to reduce PH/Alkalinity & Soda Ash to increase PH/Alkalinity - I used the Hot Tub Start Up Forum here to get this right at start up and have not had to use any of these products for the past 2-3 weeks as the PH seems locked in currently.

We are new hot tub owners and this has me stumped. I can smell the chlorine, but I barely get a reading with Jets off.

Jets off
FC - 1.0 - Also, it seems that if I let the water sit a few minutes before testing, the FC will rise by 1-2. This has never happened with the pool, so this has me stumped with the hot tub
CC - 0
PH - 7.6
TA - 50
CH - 310
CYA - 30
CSI - -.40
Temp 102degrees


Jets full on
FC - 7.0
CC - .5
PH - 7.6
TA - 50
CH - 310
CYA - 30
CSI - -.40
Temp 102degrees

 

[jseyfert3]

Did your particular spa come with ozone? I see it's an option for that spa.

 

[Brett S]

I am really baffled by this. I can’t think of any reason why the FC reading would increase while the jets are on. Especially by that much. About the only thing I can come up with is that you are adding the chlorine while the jets are off and as such the water isn’t mixed and there is a significant amount of chlorine sitting on the bottom until the jets come on to mix the water around. If you are adding chlorine and then testing the water before the jets have been run, then I think this is the explanation.

However, if this is not the case, then I’d like to see you do the following...

-Turn on the jets and test the water to verify that you’re getting the high reading.
-Then turn off the jets and wait a minute or two for the water to calm down and take another reading. I can’t imagine that this will be any different than the reading that was taken with the jets on, but it will be interesting to see what the reading is.
-Then leave the jets off and take a reading every 30 minutes for the next few hours. I’d like to see if and how quickly the reading starts to drop.

 

[JoyfulNoise]

Are you using a 25mL water sample and adding two heaping dippers of R-0870 powder? If not, please retest using the 25mL sample guidelines and ensure that you are doing the CC test IMMEDIATELY after the FC test goes from pink to clear. Do not wait between tests.