Hello I am using the BBB method in my pool and thought I would try it in my hot tub. I followed the instructions on here on how to set up the hot tub. Everything seems to be working just fine. Water is clear and smell free. However every time we test the hot tub (every day or every other) the FC level is always 0, am I doing something wrong? Is the water temp effecting the results?

thanks for any help

If possible, you may want to post a full set of test results and how you got them if you can.

Most likely is that you are not using enough chlorine to handle your bather load. I would shock to add more chlorine until you get to a situation where it holds. Then use more chlorine after your soak such that you get a measurement the next day.

The rough rule-of-thumb is that a hot (104ºF) tub needs around 5 fluid ounces of 6% bleach or 3-1/2 teaspoons of Dichlor or 7 teaspoons of non-chlorine shock (43% MPS) for every person-hour of soaking. This is just a starting point, however, since people sweat different amounts -- adjust your chlorine amount so that you measure 1-2 ppm FC before your next soak (assuming you are adding chlorine after your soak, which is what most people do). I also assume you have built up 30 ppm CYA by using Dichlor first.

It would also be useful to know how often you use the tub, if you have an ozonator, how you converted to BBB (i.e. did you drain/refill, did you do decontamination, use Spa System Flush, etc.?). Also, are you using a FAS-DPD chlorine test kit (i.e. TF-100 or K-2006) since a regular DPD chlorine test can bleach out at high chlorine levels?

Hello,

We do have our CYA at 30. I do not have an ozonator (what is this?). I did a drain and refill for my BBB switch. We use the spa about 1 -3 times a week for less than an hour with 2 to 4 people. I am using the TF-100 kit and testing the FAS-DPD way. We tested again today and the chlorine was unregister with ph at 7.9 and cya at 30

An ozonator produces ozone, sometimes spas have these to aid in sanitation.

Please try a Chlorine Demand test.
1) Add what you think is the right amount of bleach (the Pool Calculator is useful for this) to bring the spa up to FC 10. Let the pump run at least 5 minutes, then test FC to make sure it is 10. If not, keep doing the add/circulate/test loop until you do see FC 10.
2) Wait 24 hrs (do not use the tub).
3) Test FC.

Then you can convert this to a Chlorine Demand percentage. For example, if the first test shows 10.0 and the second test shows 8.0, that's a 20% demand (which is reasonable). If the second test shows 4.0, that's a 60% demand (which is too high and you should probably shock).
--paulr