Jump to content

Any Difference Between Chlorine And Bleach?


jacko64

Recommended Posts

The terms "dichlor", "dichloroisocyanuric acid", "dichloro-s-triazinetrione" and "troclosene" all refer to the same chemical which is essentially Cyanuric Acid (CYA) that has two of its three hydrogen (at the nitrogen sites) replaced with chlorine. "Trichlor" is similar except it has all three hydrogen replaced with chlorine. The typical "Dichlor" replaces one of the hydrogen of CYA with Sodium and that is what you have, plus the compound also has two water molecules attached as well (i.e. it's not pure).

The bottom line is that when you add your Dichlor chlorine granules to water, for every 1 ppm of free chlorine that is added, you also get 0.9 ppm Cyanuric Acid (CYA). The chlorine mostly stays attached to the CYA, but some of it goes into the water as hypochlorous acid (HOCl) which is the disinfecting form of chlorine.

Bleach is sodium hypochlorite (NaOCl) and when added to water also forms hypochlorous acid (HOCl), the disinfecting form of chlorine, and this mostly combines with any CYA in the water with some of it staying free to disinfect. The hypochlorous acid from Dichlor and from bleach is completely identical. So the only difference is that with Dichlor you are also adding more Cyanuric Acid (CYA).

When you measure "Free Chlorine" you not only measure the actual truly free amount of hypochlorous acid (HOCl) that disinfects, but also the hypochlorite ion (OCl-) and, mostly, the chlorine that is bound to CYA. As the disinfecting chlorine in the water gets used up, it gets replenished from the chlorine that is bound to CYA. So you can look at CYA in the water as being a sort of chlorine "buffer" that holds chlorine in "reserve".

The amount of disinfection (and oxidation) capability in your spa is related to the amount of hypochlorous acid (HOCl) only. The CYA reduces the amount of this disinfecting chlorine by roughly the amount of CYA in ppm (at a pH of 7.5). So with 30 ppm, you have about 1/30th the amount of disinfecting chlorine than you would if there were no CYA present. This is why it is very important not to let the amount of CYA get too high and this means one should not use Dichlor as their only source of chlorine or for shocking.

On the other hand, some amount of CYA is needed or else the chlorine would breakdown too quickly in sunlight or would dissipate (outgas) too quickly in a hot spa with aeration from jets. The bacteria Pseudomonas aeruginosa that causes "hot tub itch" is somewhat difficult to kill, but a combination of 4 ppm Free Chlorine (FC) with no more than 20 ppm CYA appears to be enough to keep this bug away. This means that after draining and filling your hot tub with fresh water, you should start using Dichlor a few times but not more than the amount that would result in 20 ppm FC so that you make sure you don't have more than 20 ppm CYA. Then, you switch to using bleach from then on (until you drain and refill again). You would also use bleach for shocking, if you need to. If you find that bleach alone is not sufficient for shocking (i.e. if the Combined Chlorine, CC, is more than 0.5 even after shocking) then you can use a non-chlorine shock, potassium monopersulfate (KMPS).

The bleach you should use should be unscented. Some dealers will tell you that bleach is not registered with the EPA for use in hot tubs (it is registered for use in pools), but that is not because it does not sanitize. It is simply because the market for bleach in hot tubs is very small and not worth paying for the extra registration costs -- at least that is why I believe Clorox didn't bother (consider how small the amounts of bleach are that you add to a spa compared to what you add to a pool).

Hope that helps!

Link to comment
Share on other sites

If you remove the hot tub cover about 5 minutes before you get in, that should help to dissipate any chlorine that has accumulated. You shouldn't be smelling more chlorine than you did in the first few times of using dichlor, but you will smell more than you would have if you had continued to use dichlor. You might be OK with the 3 ppm FC -- I try to be conservative when it comes to hot tub itch. If you start to smell a nasty chloramine smell (not the "fresh" smell of chlorine similar to fresh bleach), then you may need to shock. The best way to tell, is to test with a good chlorine test kit that uses drop-based FAS-DPD. Taylor has a complete kit, K-2006, that also tests pH, TA, CH and CYA (it only tests down to 30 ppm, but if it's cloudy yet you still see the black dot somewhat, then it's probably around 15-20 ppm). If you already have a kit for everything except the FAS-DPD chlorine, you can get the Taylor K-1515-A. With an accurate chlorine test, you can see if you have Combined Chlorine (CC). The test strips and other chlorine tests (OTO, DPD) are not as accurate.

Link to comment
Share on other sites

ok thanks mate will try that.think ive had that hot tub itch, had a few friends round sat night with kids aswell was too many in tub lost a bit of water , got up next morn n it had turned off due to lack of water and no chlorine levels , so i shocked it with dichlor, only had water in a week so i dont want to dump it but it seems to smell even after a good shock n 2 days later. any ideas?

Link to comment
Share on other sites

It's really hard to tell what is going on without proper testing. That's why I suggested the Taylor kits, though any you can find that are called FAS-DPD and work by counting drops you add in order to determine Free Chlorine and Combined Chlorine would be good (it's similar to the TA and CH tests in terms of adding drops and looking for a change in color -- in the case of the chlorine test, the color goes from pink to clear). You'll also want to test the CYA level even though it may be lower than the lowest measurement on the test (which is usually 30 ppm).

You see, the problem is that if you add more Dichlor, it will tie up more chlorine and that will reduce the smell (assuming it's "clean" chlorine you are smelling), but if you add too much, then you won't have enough disinfection against "hot tub itch" unless you use a lot higher FC levels. On the other hand, if the smell is the bad chloramine (combined chlorine) smell, then shocking is needed and it may be that shocking with the dichlor alone is not effective. It might take a lot of bleach -- usually 10 times the amount of Combined Chlorine.

So here are some choices. My preference would be for you to get a good chlorine test kit so you can really get a handle on your pool water and know what to do with confidence. If you don't do that or until you do, you can get some non-chlorine shock, that potassium monopersulfate (KMPS) I mentioned, and use that on a weekly maintenance dosage basis. If the smell goes away, then it was probably combined chlorine and the non-chlorine shock is taking care of it. If it doesn't, then maybe you don't have enough CYA after all and need to add some more Dichlor. The last possibility is that you actually have the right balance right now, but that the chlorine smell is "normal" for a hot tub. That's one of the reasons some people like bromine instead, but then again some people are slightly allergic to the bromine (get rashes, etc.).

Link to comment
Share on other sites

One thing that might help with the chlor. smell. We use bleach only and have discovered that if we put it in right after using the tub and also again in the morning before work that there is no smell. If we wait till we get home. Then on those night there is a strong odor of chlor. [ bleach] Chem geek is right about opening the cover 5 minutes before you get in.

Link to comment
Share on other sites

thanks to you both for all this good info. how much bleach do u put in each time and how many gallons is your tub turbottt? i put 1/3 pint of less than 5% in after i came out of tub last night , checked it this morning and its showing no total or free chlorine . so ive just added a little dichlor cos i know that will bring up the readings . still unsure about bleach.

jacko

Link to comment
Share on other sites

Adding 1/3 pint of 5.25% bleach (which is a little more than your strength) to 350 gallons would increase the FC by over 6 ppm which is quite a lot, especially if done every day. In 500 gallons, it would increase FC by about 4.5 ppm. You could check the chlorine level after adding the bleach and letting it circulate for a few minutes (with some jets on). That'll give you a better idea of the true strength of your bleach and how much the FC goes up with the 1/3 pint you add. Maybe you have the very inexpensive 3% bleach. I would have speculated that its strength was very, very low, but you said you noticed a chlorine smell after adding it.

So something doesn't make sense. If there were very little or no CYA in the hot tub, then the chlorine you add would outgas from the tub rather quickly, but with CYA in the tub it shouldn't leave that fast, especially if you put it in AFTER you got out of the tub, turned off the jets, covered the tub (do you cover it?), then tested in the morning. If the chlorine were to leave quickly, it usually would happen with the cover off and the jets running.

What kind of chlorine test are you using? Some of them will bleach out with too high chlorine levels having you think there isn't any chlorine when there is actually a lot. The DPD (red color) chlorine test can do that above 10 ppm FC. The OTO (yellow color) chlorine test should be OK with higher chlorine levels (the FAS-DPD test is also OK as it has a flash of color when you add the powder so you can add more if the chlorine is very high). If you are using the DPD test, then you can dilute one part of your spa water with several parts of distilled water (or filtered water) and retest -- if it turns red, then very high chlorine levels were present. That would be more consistent with the strong smell you are experiencing (i.e. maybe you were adding too much bleach and weren't aware of that).

Link to comment
Share on other sites

We have a 450 gal spa. [ Our fresh water supply is from our pool] On fill we add three cups ultra unscented. Heat the water and then do our other adjustments. With fresh bleach in new water we add a half of cup after were all done for the day and then in the morning we do the same. As the water or bleach gets older we increase the amounts at least to 3/4 of a cup each time. Once a week we add just a touch of ph down and I like the ta to be aprox. 70-80ppm. We do have a ozonator and I believe it effects our chlor. quite a bit. We also at least once a week hose our filter out. With using bleach there is a deposit left on the filter.[ looks like spent salt???] Maybe chem geek can explain this. Hope this helps. steve

Link to comment
Share on other sites

If the Ultra bleach says 6%, then 3 cups in 450 gallons is 25 ppm FC which is really more like a shock than anything else. The half a cup is 4.3 ppm FC and you are adding that twice a day. That is an awful lot. The reason is that you don't have any CYA (it sounded like you don't use Dichlor at all) so the chlorine outgasses very quickly in that case. I'm surprised you don't smell it more. It's also rather hard on your swimsuits at these higher concentrations (without CYA, the disinfecting and oxidizing chlorine concentration is about 20 times higher than the same amount of chlorine with 20 ppm CYA). I would suggest that when you do a fresh fill (or even now with your current fill) that you use Dichlor for a few days for the equivalent of around 15-20 ppm FC. I'll bet your chlorine loss will go down quite a bit after you've used the Dichlor. And yes, you are right that the ozonator may also be lowering your chlorine level somewhat, but I'll bet the bulk of your loss is due to not having CYA in your tub.

As for a deposit on the filter, there shouldn't be any if the bleach is unscented. You shouldn't use bleach that is scented or perfumed because it will leave gunk in the filter. Unscented bleach is only sodium hypochlorite and salt. The sodium hypochlorite converts to salt when it gets used up so you just end up with salt and that won't show up in the filter or anywhere else. So if you are using unscented bleach, then the filter gunk is a mystery.

jacko, before you switched to trying out bleach, how much Dichlor did you add every day? Maybe your chlorine demand in your spa is just high and it needs a lot of chlorine from any source, Dichlor or bleach, each and every day.

Link to comment
Share on other sites

i put a tea spoon in every day and a bit more if i had a big bather load, after i put dichlor in this morning i ran the jets for 1/2 hour and it showed between 5 and 10 on the test for both total and free chlorine. 8 hours later tested again and the free chlorine is 3ppm but total is still high ish about 7. ph and alk are good a tad low if anything but still in range.wot would happen if i just used dichlor all the time, which is what i did for the first 2 months then after water change i read about using bleach.

Link to comment
Share on other sites

I don't know your hot tub volume, but assuming it is 350 gallons, then 1 teaspoon (not tablespoon) of Dichlor would add about 2 ppm FC (and 1.6 ppm CYA), but you saw much more than that (5-10). Something is really weird here -- there's some information missing because it just doesn't make sense. Are you sure it wasn't a tablespoon you added?

If your total chlorine is 7 when your free chlorine is 3, then you have a lot of combined chlorine (4 ppm) and if that is monochloramine, then that smells pretty bad (like a heavily used indoor swimming pool). The chlorine you are adding to your spa, whether it be Dichlor or bleach, is getting consumed by something in your spa. If it were just getting outgassed, it wouldn't raise the Total Chlorine. The chlorine alone is not shocking your spa, but just adding Dichlor won't do that either. You may need to use a non-chlorine shock (potassium monopersulfate, KMPS) and that would be true regardless of whether you used Dichlor or bleach or a mix because your chlorine is not breaking down organics (or ammonia) sufficiently (without exposure to sunlight, this can be difficult -- it takes time and if you use your hot tub frequently, then the non-chlorine shock would be the way to go for shocking -- it breaks down organics readily while chlorine does not, at least not without sunlight).

As for what would happen if you just use Dichlor only, your Cyanuric Acid (CYA) level would build up and would combine with chlorine more (including the chlorine that comes from Dichlor itself) so that the amount of disinfecting chlorine in your hot tub would be less and less over time, assuming you kept the same Free Chlorine level. You can compensate for this by increasing the Free Chlorine level. So if you had 3 or 4 ppm FC at 20 ppm CYA, then after another week of Dichlor you would need 6-8 ppm FC at 40 ppm CYA and after 2-3 more weeks you would need 12-16 ppm at 80 ppm CYA and so on. It's not practical at some point so what happens after a month or so is that your disinfecting chlorine level will not be high enough to kill the bacteria that causes "hot tub itch". It should be plenty high enough to kill other bacteria and viruses.

Link to comment
Share on other sites

Yes, if your CYA is very high, then 5 ppm FC may not be enough to prevent "hot tub itch" though it should be enough for most everything else. If you have a CYA of 90 then it would take 15 ppm FC to be equivalent in disinfecting and oxidizing power as 5 ppm FC with a CYA of 30 (roughly speaking -- and at a pH of 7.5).

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Unfortunately, your content contains terms that we do not allow. Please edit your content to remove the highlighted words below.
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
×
×
  • Create New...