Combined Chlorine Issue.

[robquick]

Hi,

I recently purchased a professional water testing kit and was surprised having tested the water that my combined chlorine was 2.8ppm. I took the test kit back to the shop with a water sample and got the shop to test the water with my kit to ensure I was following the right process. They tested the water at the same level and then tested on their in house equipment which again tested at the same level.

I'm religious with testing and adding chlorine on a daily basis, I also follow the 3.5 teaspoons per bather hour immediately after bathing (adjusted slightly down to compensate for Ozone). What am I doing wrong that has allowed my CC to get so high and what can I do now to resolve quickly? I regularly have chlorine levels over 20ppm immediately after bathing so I'm not really sure what else I can do.

Finally what is an acceptable level for CC? My understanding is under 0.5ppm.

Thanks.

[chem geek]

Are you using Dichlor-only? If so, how much have you cumulatively added to your spa? Are you using the tub every day? Dichlor increases the CYA level in the water. For every 10 ppm Free Chlorine (FC) added by Dichlor, it also increases Cyanuric Acid (CYA) by 9 ppm. Over time the higher CYA level will lower the active chlorine level so it can slow down oxidizing your bather waste to the point where you will get behind even if you are adding the proper amount.

This problem can be avoided by using the Dichlor-then-bleach method instead. With this method, the CYA won't build up so the active chlorine level remains fairly constant.

Also, be sure to take your water sample before your next soak, not after a soak. The CC will rise during and after a soak and will drop down as chlorine oxidizes the bather waste.

[robquick]

CYA is 85 and I've been using Calcium-Hypo for the last two months, I use the tub about 2 or 3 time a week for 30 mins with 3 people.

What's the best way to recover now?

Do you think the CYA is causing the problem ?

Thanks.

[chem geek]

Your bather load at around 3-3/4 person-hours per week is somewhat high, but not extraordinary, so maybe in combination with the higher CYA then the chlorine is having trouble keeping up. However, it could be that the people are bringing in slow-to-oxidize organics such as those from lotions. Hard to know. You could try replacing your water or at least half or two-thirds of it. If the CC starts to drop, then the higher CYA or sheer quantity of things to oxidize were an issue.

Don't forget that for every 10 ppm Free Chlorine (FC) you add of Cal-Hypo, it also increases Calcium Hardness (CH) by at least 7 ppm. So be careful about your pH and TA since if those go up with the higher CH, you could get calcium carbonate scaling, especially in your heater.

[robquick]

Thanks.

I've just ordered the bleach that you posted about earlier in this thread. Can bleach be damaging to any type of shell (not sure what mine is).

Is there nothing I can do with Shocking or super chlorinating now?

[chem geek]

So long as you add the bleach slowly when the circulation pump is on, then there is no problem with any sort of spa material. You just don't want to dump it in quickly with no circulation since it is denser than water until it is mixed so would settle at the bottom. With circulation, it mixes and will stay mixed.

You can try to raise the Free Chlorine (FC) high to try and lower the CC but it sounded like that wasn't working well. You can certainly try it again if you want to. A shock level is around 40% of the CYA level so at 85 ppm that would be 34 ppm. If you later on want to get the FC lowered faster since it may stay up for longer than you'd like, you can use a dechlorinator to lower it -- hydrogen peroxide will do the trick. It takes roughly the same volume of 3% hydrogen peroxide to lower a volume of 6% bleach that was added. You can use http://www.thepoolcalculator.com'>The Pool Calculator to calculate dosing.

[robquick]

I took my professional water tester back to the shop today and they checked the calibration in front of me with 'references' that the manufacture supplied. The tester was way within the tolerances described by the supplier and therefore appears to be accurate. This leads me to ask a few more questions about CC which I don't seem able to reduce below 2ppm regardless of the level of chlorine added.

When hot tub water has been used for a while and is getting closer to the end of its life would you expect CC to be higher than on day one?

When using older water do you get to a point where CC can't be reduced back to normal levels IE below 0.5ppm?

The reason I ask the question is that my local pool store told me that CC is made up of organic and inorganic matter. And that organic matter can't be completely got rid of and over time with bathing will slowly increase !!!!! Is this true, if so, this would explain my high CC ?

To get to the bottom of the CC level that my tester is reporting I tried a test with tap water today. I added about two granules of Dichlor to 300ml of water and then took FC and CC readings. The FC was 2.09ppm which was what I expected the CC measured at 0.39ppm, would you expect the tap water to have CC levels that high ?

Any support appreciated.

[chem geek]

Yes, water that has accumulated hard-to-oxidize organics could build up some that register as CC. If it doesn't smell, then I wouldn't worry so much about it since it could be CC that isn't volatile nor irritating. For disinfection purposes what is important is that you measure FC. The CC won't interfere with chlorine -- it just can't be counted on by itself to disinfect.

As for tap water, the CC amount depends on whether or not it is chloraminated since some tap water has monochloramine added to it, though usually you'd see that level at around 1 ppm or so. Your tap water sounds like chlorine was added, hence the FC, so the CC is coming from chlorine reacting with something in the pipe. Yes, that can happen. Do you get FC with a little CC if you just measure the tap water without adding any Dichlor to it?

[robquick]

Hi Chem Geek,

Tap water measured as follows.

FC - 0.53ppm

CC - 0.15ppm

TC - 0.68ppm

Do these numbers make sense ?

Thanks.

[chem geek]

That's possible for tap water that was chlorinated and lost some FC as it went through the pipes and reacted with some chemicals in the pipe that results in some CC. So this would seem to indicate that the CC you are measuring in your spa water is real, though as I noted it may not be a problem. If you don't smell it and if you are still able to have an FC level, then your're still OK. It will be interesting to see what happens after a water change and how long it will take before the CC level rises again.

[barlav]

I am experiencing the exact same issue with CC and wasn't sure why. I am ending my first full Dichlor/Bleach cycle (which I couldn't be happier with btw). I am at 6 months with current water and, other than a 2ppm CC reading, everything is like it was on day one. Crystal clear, smell and foam free even with daily use of the spa. FC has never dropped below 2 and CYA has always remained less than 30. Since I haven't noticed any chloramine smell I am thinking it must be just the age of the water and the hard-to-oxidize organics that must be contributing to the CC readings? I don't use MPS, just dichlor and bleach and occasionally some dry acid to bring down the alkalinity that gradually creeps up. I have shocked it also but that didn't help. I left the cover off for a day also and CC came down a little but not much. It is time for a water change and now I'm just waiting for a nice enough day to do it so I figure once I do a flush of the system and put new water in the CC will go back to 0.

Maybe a CC reading like this could be used an indicator for when it is a good time for a water change for the dichlor/bleach method? Since, like I said, there really was no other indicator that the water needed changing (other than it being 6 months old!)

[chem geek]

Yes, what you describe sure does sound like it's just the slow buildup of slow-to-oxidize organics, but ones that aren't particularly volatile and not really any sort of problem. I suppose you could use it as an indicator for a water change, but not sure exactly what to recommend for when to change it. By the way, since it sounds like you may have used the spa every day, what was your average daily bather load in person-hours? Also, what is your spa size in gallons? It would be interesting to compare how long you've gone against the Water Replacement Interval (WRI) used by the spa industry which in person-hours is (1/9) x (Spa Size in Gallons) / (Person-Hours Per Day). With Dichlor-then-bleach I've usually said that one can go at least twice as long as this formula would indicate, but it sounds like you've gone much longer than that.

[barlav]

It is a 450 gallon SPA and the Person-Hours Per Day average over the last 6 months is probably 3/4 to 1. When switching to dichlor/bleach I was hoping to be able to get about 6 months out of it to prevent having to do a water change during cold winter weather months. October and April was the plan for water change times. Since 6 months is quite a bit longer than the recommended WRI should I reconsider and do it more often?

[chem geek]

So the standard WRI (converted to use person-hours) would be (1/9) x (450) / 0.75 = 67 days and with Dichlor-then-bleach we usually expect to be able to get at least double that so 133 days or around 4-5 months (and if you were 1 person-hour per day it would be even less at 100 days or 3-4 months), then going for 6 months is indeed beyond this. However, this is not a problem. I was only estimating roughly, but more than one person has reported being able to go more than twice as long. So I think you're fine, especially since you don't notice any smell or other side effects -- just a reported CC reading.

The only other issue would be a build-up of salt, especially if one does not have an ozonator. I forget -- do you have an ozonator? If you don't and you use the standard recommended amount of chlorine to oxidize bather waste, then this translates to about 5.4 ppm FC in 450 gallons per person-hour. So over 6 months with 1 person-hour per day that would be 972 ppm cumulative FC resulting in 1.65*972 = 1600 ppm sodium chloride salt. Some spas have lower quality stainless steel components so might get corroded faster at higher salt levels. So to play it safe, you probably shouldn't go too much longer between water changes. Note that some saltwater chlorine generators for spas use 2000 ppm, but they are not suited for all spas. Note that the buildup of salt is faster in a smaller spa (at the same bather-load) so yours being 450 gallons is helping you out somewhat.

[barlav]

Yes, my spa does have an ozonator. I was wondering about the salt too. The spa is a Hot Springs Envoy. They tried to sell me a salt water sanitizing system for the spa but I wasn't interested but, because of that, I am assuming this spa would be one built to handle a higher level of salt. I am glad to know that 6 months is going to be workable because that works out really great. Thanks for the great info!

[chem geek]

So if you were adding, say, half the amount of chlorine because of the ozonator, then your added salt would only be half as much or around 800 ppm which shouldn't be any problem at all. And as you say, if they were proposing a salt-based sanitizing system then yes, the spa can probably handle higher salt levels.

It's interesting that in spite of having an ozonator that CC can still build up. Ozone and even the hydroxyl radicals that are produced when it breaks down do not oxidize everything. Some chlorinated organics or whatever is showing up as CC is simply not reacting with either chlorine or ozone.

[barlav]

I am going to change the water this weekend. Out of curiosity I ordered a TDS meter. I want to see what it reads before and after the water is changed and balanced. I added enough bleach for daily bather load as well as extra to keep it > 0 until the next use. 10oz of 6% bleach each evening after use gave me a FC of 2-4 24 hours later prior to next use. Also shocked a few times. I am thinking based on that amount of bleach the salt is probably higher than 800.

[chem geek]

10 ounces of 6% bleach is 10.7 ppm FC so after 6 months that would be 1.65*10.7*6*30 = 3180 ppm salt. That's very strange that with only 1 person-hour of soaking that you needed that much bleach given that you have an ozonator. I wonder if the ozonator was actually working. And even without an ozonator one person-hour would normally need more like 5 ounces of 6% bleach, not 10 ounces. You are sure that the bleach was 6% and not 3%? Off-brand regular bleaches are often only 3% -- it's the off-brand Ultra bleaches that are 6% and the Clorox Regular (Clorox Ultra in Canada) that used to be 6% and is now 8.25%.

[barlav]

I used Clorox Regular 6%. I thought I needed to add above and beyond the amount for the bather load to keep the FC up between soaks (which is 24 hours) beacuse of the ozonator? The ozonator seemed to use the bleach when not soaking at a rate of about 50%. As far as I know the ozonator has worked all along. Maybe I don't need to add that much? I just didn't want the FC to drop to 0. Going to change water today and then maybe use TDS meter next time to determine when to change water so it doesn't get so high.

[chem geek]

You are right that you need to target the FC so add whatever bleach amount was needed for that and you are right that with an ozonator the chlorine demand is higher when there is no bather load, but if you were soaking every day then usually the chlorine demand is lower with an ozonator because the ozone oxidizes some of the bather waste so that chlorine doesn't have to. That's what we usually see.

So maybe for whatever reason in your situation the ozonator is increasing chlorine demand even when you use the spa every day. That seems strange. You would have been better off not having the ozonator on at all which may have let you use around half as much chlorine. Unless there's something else going on. It is true that as the water builds up slow-to-oxidize organics the chlorine demand will increase -- was this 10 ounces an amount that was needed even early on in the first month or so after the last water change? Or did it start out lower and end up at 10 ounces?

By the way, though a TDS meter is OK, they can be finicky and inaccurate. I use the Taylor K-1766 salt (chloride measured as ppm sodium chloride). Each drop in the test is 200 ppm and it's fairly accurate. One can use a 25 ml sample size instead of the 10 ml in the instructions and use 2 drops of indicator dye and then each drop of titrant will be 80 ppm salt.

[barlav]

Thanks for the info wizard and chem geek. I just finished up with the water change. This is the TDS meter I bought: http://www.amazon.com/gp/product/B0002T6L5M/ref=oh_details_o01_s00_i00?ie=UTF8&psc=1 The product specs on the company's website said it can be used for pools/spas. So for whatever it's worth I tested the old water (4540 ), the tap water (180) and the new water after it was completely balanced and after initial shock (530). I added dichlor for shocking, dry acid to bring down TA, some Calcium and borates so that took me from 180 to 530. So I definitely let TDS get out of hand these past 6 months. I was so busy concentrating on perfect water chemistry using dichlor/bleach I really had no idea about TDS and that it shouldn't get too high. So at least I can use it as a guide. If it gets over 2000 (I read somewhere that going until 1500ppm over the initial reading after balancing is a good bet) then I will consider doing a water change or at least a half drain/fill. I have learned from this that maybe letting the water go for that long with heavy use probably isn't ideal. Even though everything seemed great water wise I also don't want the equipment to wear down because of a high TDS.

I popped off the front panel and I couldn't see anything that would indicate that the ozonator isn't working. There is no light on mine, I was hoping there was some kind of indicator other than the bubbles. Spa is less than a year old so at this point I will assume it is working. The ozonator I have is a watkins fresh water III (http://shop.prescottspas.com/products/hotspring-freshwater-iii-ozone-ozonator) From what I've read I guess it is pretty powerful so maybe it uses up a lot of chlorine in between soaks?

Oh, and now CC is back to 0 of course

Thanks again for all this great info! This forum is terrific and I feel like I have a good knowledge of my spa and it's water now.

[chem geek]

I wouldn't worry about the 1500 ppm TDS rule. It's just a proxy for organic load but normally TDS is not an issue. The only thing is that the greater conductivity can be more corrosive to metal, but it really depends on the quality of the materials in the spa. Probably a good idea for you to change the water now anyway as you did, but if you change it at 2000 ppm then that may be after only 3 months. Too bad we can't figure out why the chlorine demand is so high. Did you ever do a 24-hour chlorine demand test when there was no bather load, preferably at least 2 days after the last bather load?

[barlav]

Does the 24-hour chlorine demand test work right after a new fill? If so, I shocked to 15ppm using dichlor after filling and 22 hours later it is 4ppm (CC still 0). Spa has not been used since fill and has been covered. Could it just be the ozonator just eats it up? I am wondering if I can get away with just using less going forward. If I add 5ppm after 1 person hour each day I imagine the FC will drop to 0 by the next day's use but maybe that isn't the end of the world because of the ozonator?

[chem geek]

Yes, normally the test should work well on a new fill, though there might be monochloramine in the tap water, but usually not more than around 1 ppm or so. So yes, 73% loss in 22 hours is high, even for an ozonator. It's still possible that you've got biofilms in the piping creating a large chlorine demand, but if it's always been this way and you used Spa System Flush at some point, then it's more likely to be the ozonator.

The ozonator won't prevent bacterial growth on spa surfaces unless it keeps enough ozone in the water and there shouldn't be any when it's off. I wouldn't let the chlorine get to zero, especially since you wouldn't know how long it was that low. If there were a way for you to lower the ozone output, perhaps by having less frequent circulation time (if the ozonator is on when the circulation pump is running), then that might help.

[barlav]

I did use a spa flush. There were about 2 person hours of bather load yesterday. I put just enough dichlor in for the bather load yesterday which was 1.25oz (I used 6ppm/person hour). This morning I tested and FC was still at 5 so maybe things are starting to even out now. I think I will just do what I've been doing making sure the FC remains above 0 since it seems to work other than the quicker increase in TDS. The tap water had a FC of 0.5 or less and CC of 0 when I tested it. The taylor test kit makes all this a lot easier. I will still try for 5-6 months between water changes with maybe a 1/2 drain/fill in between to keep TDS in check.