Questioning My Chlorine Demand Results

[Koolbreez]

I've had my spa for about 6 months now and have just done my second refill. After much reading here I am planning on implementing the dichlor/bleach method, and though I may have some questions regarding water balance later, my concern now is the sanitation part of the equation.

After my refill, I got my water close to balanced with a CSI from the pool calculator of -0.19. I will continue to work toward 0 but I thought that this was close enough for now and shocked with dichlor. My aim was 10 ppm FC, but I wound up at 12 ppm. After sitting unused for ~24 hours I retested and my FC was 4 ppm. This means my freshly filled, 6 month old spa is using 66% of the free chloride I introduced last night. This seems troublesome to me and I wonder what might be causing this. My Combined Chlorine was only 0.5, so that seems ok. Any thoughts on what might be happening or follow up ideas would be appreciated.

Secondarily, when I test FC with the Taylor kit I reached the clear color endpoint, but then when it sat for a couple of minutes a pinkish hue developed and I added another drop, and then again, adding another 1ppm. Is this right or should I have ended at the first stop?

[chem geek]

Do you have an ozonator? It could be that it is consuming the chlorine though usually that just has it be a chlorine demand of around 50% instead of 25%. It's possible that you've got some biofilms that have developed, possibly due to Dichlor-only (if that's what you were using) that would have raised the CYA level and had rather low sanitation after 6 months -- you must not use your spa very much to have the water last that long. Were you using Dichlor-only the last 6 months or were you using something else? Did the chlorine ever get to zero for some time?

If you wait too long for the FC test, the clear can turn pink when CC is present. If what you described occurred after the CC test, then it could be that there is some slow to register CC or some other interference -- I would just count when it goes clear after stirring for a few seconds (i.e. don't wait too long after that).

[simonc]

If you wait too long for the FC test, the clear can turn pink when CC is present. If what you described occurred after the CC test, then it could be that there is some slow to register CC or some other interference -- I would just count when it goes clear after stirring for a few seconds (i.e. don't wait too long after that).

I also had a "strange" experience measuring CC's with my Taylor K-2006 kit. I measured it as 1ppm (2 drops x 0.5ppms). I put the cylinder down for a few moments still containing the test water. I noticed that some of the pink color had come back. I added another drop. It disappeared. Just for fun ... I let it sit longer and again it turned pink. I did this over and over again. Each time it took longer to turn pink, but it did turn. At my 8th drop (about a 10 minute wait after the 7th drop), I got bored of the "game" and tossed the water out. I don't believe that I had CCs at 4ppms (8 drops x 0.5ppm). If I did, it wouldn't have turned clear after just two drops.

I put in some MPS and decided not to worry about it.

- Simon

[chem geek]

I also forgot to mention that MPS will usually measure as CC.

I wonder if there's something about the CC test that doesn't "hold" well. I agree with you that it's unlikely the CC was really as high as the returning pink would imply.

[Koolbreez]

Thanks for your replies. I do have an ozonator which runs continuously, so that could account for some FC loss. I was usiing Dichlor only previous to this fill and was honestly not measuring frequently and then with strips. I had been led to a "set it and forget it" approach from my spa dealer and was just shocking with a capful of dichlor weekly. So it seems possible that there is some biofilm build up from low sanitation. (This is actually my second refill, once at 3 months and a second time now at 6 months, which I thought was a normal amount of time.) Now my question is how to eliminate it? Can it be gotten rid of with good sanitation practices from here on out or shocking to 10 on subsequent days until I see my CD go up?

[Koolbreez]

Another thought just occured to me. What about filter cleanliness? I've just been hosing them off about every other week and with my refills and not really spending a ton of time about it. I know I'm getting the surface dirt, but it seems possible that there may be some deeper dirt I'm not getting cleaned out with the hose. Could this be part of my problem?

[bart6453]

Another thought just occured to me. What about filter cleanliness? I've just been hosing them off about every other week and with my refills and not really spending a ton of time about it. I know I'm getting the surface dirt, but it seems possible that there may be some deeper dirt I'm not getting cleaned out with the hose. Could this be part of my problem?

I have found that on a fresh fill....no matter how quickly I re-fill my tub....it uses about 8ppm FC overnight. After that it stabilizes out to the 20% mark or so.

I usually bring it to 10ppm FC and have a residual of 2ppm FC.

As to filter cleanliness...YES. I have a thread somewhere on here exactly about that.

I found that as my filters get more and more dirty my chlorine demand moves upwards. I change the filters when it is at 45% and it immediately drops down to the 20% mark after a filter change.

I have two sets of filters, and the dirty ones I clean by soaking in TSP for about 4 hours and then rinse them off very, very well. I use my bathtub to soak and rinse. After that I just let them dry and put them on the shelf until my CD rises.

[simonc]

I found that as my filters get more and more dirty my chlorine demand moves upwards. I change the filters when it is at 45% and it immediately drops down to the 20% mark after a filter change.

I think the "theory" behind filters increasing the CD is that the filters capture organic material - dead skin cells, hair, bugs, etc.. These organic materials decompose in the warm tub water and this uses up more and more chlorine over time. It's a theory. I don't think anyone has tested it to see if it is true, but it does make sense.

- Simon

[Koolbreez]

@Bart - I'm glad to hear your experience with a fresh fill, I'm hoping mine is similar. I think I will add to 10ppm FC again tonight and see if it stabilizes to a more reasonable CD. I was kind of wondering if it was something from the hose being eaten up on the first "shock." I think I'll also give my filters a little better going over with the hose, pleat by pleat. A second set seems like a good idea, as well. Any links to good (cheaper than my local dealer) online places to get filters?

[bart6453]

@Bart - I'm glad to hear your experience with a fresh fill, I'm hoping mine is similar. I think I will add to 10ppm FC again tonight and see if it stabilizes to a more reasonable CD. I was kind of wondering if it was something from the hose being eaten up on the first "shock." I think I'll also give my filters a little better going over with the hose, pleat by pleat. A second set seems like a good idea, as well. Any links to good (cheaper than my local dealer) online places to get filters?

I would use some type of a filter cleaner too....I like TSP because it works and is fairly inexpensive. Just make sure to rinse the filters very, very well otherwise you will get some foaming.

[Fry Man]

I have been having the same problem of the water sample turning pink after initially going clear. I have repeater the drops to clear about 4 times before it goes clear. I assume from the other replys that the CC count should be only to the first clear state is this correct? My CC is usually 2 ppm and I have shocked to 28 ppm with no real effect. I have measure CD and it is around 17%. My filter is a disposible one and has been the SPA for 3 months. The CC level has been constant for most of the time. The water balance has been constant for the past 3 weeks with very little movement. My FC is usually 6-7 ppm from an SWG system with an Ozonator. When should the filter be replaced?

[bart6453]

I have been having the same problem of the water sample turning pink after initially going clear. I have repeater the drops to clear about 4 times before it goes clear. I assume from the other replys that the CC count should be only to the first clear state is this correct? My CC is usually 2 ppm and I have shocked to 28 ppm with no real effect. I have measure CD and it is around 17%. My filter is a disposible one and has been the SPA for 3 months. The CC level has been constant for most of the time. The water balance has been constant for the past 3 weeks with very little movement. My FC is usually 6-7 ppm from an SWG system with an Ozonator. When should the filter be replaced?

I have been changing my filters once my CD goes up to 45% or at the 3 month mark....whichever comes first.

[PaulR]

If you wait too long for the FC test, the clear can turn pink when CC is present. If what you described occurred after the CC test, then it could be that there is some slow to register CC or some other interference -- I would just count when it goes clear after stirring for a few seconds (i.e. don't wait too long after that).

I also had a "strange" experience measuring CC's with my Taylor K-2006 kit. I measured it as 1ppm (2 drops x 0.5ppms). I put the cylinder down for a few moments still containing the test water. I noticed that some of the pink color had come back. I added another drop. It disappeared. Just for fun ... I let it sit longer and again it turned pink. I did this over and over again. Each time it took longer to turn pink, but it did turn. At my 8th drop (about a 10 minute wait after the 7th drop), I got bored of the "game" and tossed the water out. I don't believe that I had CCs at 4ppms (8 drops x 0.5ppm). If I did, it wouldn't have turned clear after just two drops.

I put in some MPS and decided not to worry about it.

- Simon

My understanding is that if the pink is gone for 5-10 seconds, that's good enough to call it a reading, and not to worry if the pink reappears after longer than that.

--paulr