With Dichlor-then-bleach Method

[cpuKEN]

I'll certainly go back and review the Dichlor-then-bleach document but thought I might get a quick answer for this question. With this method does one need to be concerned with the Combined Chlorine levels or the MPS levels.

Test strips the last two days indicated low levels of MPS and my Combined Chlorine levels are zero or just above.

thanks

Ken

[chem geek]

Ken,

First of all, you should be aware that MPS registers as Combined Chlorine on such tests unless you use a special test interference remover. Also, test strips are notoriously inaccurate in general.

If you go with a chlorine sanitation approach, such as Dichlor-then-bleach, you should definitely get yourself a Taylor K-2006 test kit since it is far more accurate than test strips and even standard DPD chlorine tests. It can measure Combined Chlorine (as well as Free Chlorine) with an accuracy of 0.2 ppm when using a 25 ml sample size.

It is unusual to see combined chlorine readings above 0.5 ppm when using the Dichlor-then-bleach method except during and soon after a soak when such readings would normally be expected due to bather waste (especially right after a soak since most people start their soak with 1-2 ppm FC and only add Dichlor or bleach after the soak). Some number of hours after the soak, the bather waste is oxidized so that by the time you soak again the CC level is low.

With Dichlor-then-bleach, one does not need to be concerned with the MPS levels since one usually does not use MPS with that method. Even if you did decide to shock once a week with MPS, you wouldn't normally test for the MPS level and would just remember that any CC reading in the day or two after adding MPS is a falsely high reading due to the MPS.

Richard

[Dnepr Dave]

I use the dichlor-then-bleach method. I don't use MPS in my spa.

Dave

[Ep7735]

well, we've just drained and cleaned our hot tub, and we were going to switch to the dichlor/bleach method. I ordered the taylor test kit you mentioned a few days ago, so that I would hopefully keep up with the maintenance better than in the past. but, my tub has an ozonator and i read that people have problems with this method if their tub has an ozonator - and I'm about to have surgery away from home and won't be able to check my tub every day - like what it seems is required for this method, especially in the beginning.

so we've decided to keep on with bromine - but now i'm wondering if I ordered the wrong test kit or if it will work for both? if it is wrong, is there some cheap component i can buy to make it work and not have wasted that money?

thanks for any help!

[chem geek]

You can use the chlorine test with your bromine spa (I assume it's a Taylor K-2006 that you ordered). You need to do two things. First, is that you want to add the R-0003 reagent after you've added the DPD powder. This is because you don't care about a Free vs. Combined Bromine reading -- only Total Bromine matters since bromamine is also a reasonably effective sanitizer. Second, is that your FAS-DPD test for a 25 ml sample has each drop represent 0.45 ppm bromine while with a 10 ml sample each drop represents 1.125 ppm bromine. That is, the bromine reading is 2.25 times the chlorine reading (because the units of measurement are different).