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  • 3" Chlorine Tablet in Skimmer

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Thread: Chlorine tablets over chlorinating in-ground-spa. Best way to chlorinate?

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    Chlorine tablets over chlorinating in-ground-spa. Best way to chlorinate?

    I just refurbished my spa by tiling over the plaster/concrete. I have had the spa for years and prior to tiling, I may not have had any problems using tablets of chlorine, as I just put a 3" tablet in the skimmer.
    When I refurbished the spa, I did extensive research about chemicals and have been reading this forum in particular and it appears that putting the tablet in the simmer may be a bad idea. So, I have been using a small float to chlorinate the spa.

    I read on this forum that the best solution would be to use liquid chlorine bleach. However, because I have always used 3" tablets in the past and was running out of tablets, I bought 50 pounds because the price was lower to buy a larger quantity. So, now I need to use them up.

    The problem I am having with the float is that when I put it in the spa, the following day the spa test shows that it is over chlorinated. Therefore, the next day I have to take it out and wait a few days for the chlorine levels to fall and then I put it back in the spa... and endless cycle.

    I have reduced the cracks in the float to the smallest limit, but does not help.

    I am using a small spa size float, but the 3" tablet do not fit so, I cut the tablets into smaller pieces. This may be one of my problem because of the surface area may be increased on the tablets, but I really do not think so. However, if that is the problem, I can buy a larger float and not cut up the tablets.

    I am not sure it would be a good idea, but I can try putting the 3” tablets in the skimmer again, but I have read that is not a good idea and I am not sure it that will solve my issue, as until now I did not know I had a problem and I may have had this problem for years. Until now, I did not test as much and the testing reagents I was using may have been old. Now, I am using new reagents.

    So, I am not sure what I should do now, as I do not want to through away 50 pounds of tablets and use bleach.

    Thank you in advance for a suggested solution.
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    Re: Chlorine tablets over chlorinating in-ground-spa. Best way to chlorinate?

    Welcome to TFP!!!

    You do realize that that is the wrong reagent for that chlorine test block right? The yellow reagent is for the OTO chlorine test and that pink block is for the DPD chlorine test. Although it is certainly still showing on the 3-5ppm side.

    What you need to realize is that that FC level may not be in fact too high. The required FC is a function of the stabilizer (CYA) level. See the FC/CYA Chart. Those tablets add chlorine and stabilizer and lower the pH. The more tablets you use, the higher the CYA will become and the higher you will need to maintain the FC level. Until eventually the CYA is so high that the tablets do not maintain a high enough FC level and your water turns cloudy/green. This is why we do not recommend exclusively using tablets for pools or for spas.

    One advantage for a spa is when the CYA gets too high, it is easy enough to drain and start over, but you need to be tracking the amount of trichlor tablets you are using to know the CYA level or be testing for it.
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    Re: Chlorine tablets over chlorinating in-ground-spa. Best way to chlorinate?

    Quote Originally Posted by jblizzle View Post
    Welcome to TFP!!!

    You do realize that that is the wrong reagent for that chlorine test block right? The yellow reagent is for the OTO chlorine test and that pink block is for the DPD chlorine test. Although it is certainly still showing on the 3-5ppm side.

    What you need to realize is that that FC level may not be in fact too high. The required FC is a function of the stabilizer (CYA) level. See the FC/CYA Chart. Those tablets add chlorine and stabilizer and lower the pH. The more tablets you use, the higher the CYA will become and the higher you will need to maintain the FC level. Until eventually the CYA is so high that the tablets do not maintain a high enough FC level and your water turns cloudy/green. This is why we do not recommend exclusively using tablets for pools or for spas.

    One advantage for a spa is when the CYA gets too high, it is easy enough to drain and start over, but you need to be tracking the amount of trichlor tablets you are using to know the CYA level or be testing for it.
    Thank you for the quick reply. yes, I do know I am using a test indicator. However, I do not see the difference, as I have one that is yellow and the intensity is the same.

    I must admit I am just a bit confused because I am not familiar acronyms: FC and CLA - what Does FC Stand for. I think FC may be the total amount of chlorine? From your chart, I see that CYA stands for stabilizer. I did know there was a stabilizer in the tablets. Is there a (CLY) in bleach?

    How do I test for a CYA?

    If my FC (?) is not too high, how do I test for the total amount of chlorine, as it appears what I am testing it not accurate.

    I am VERY confused on what to do. Thank you for your help.

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    Re: Chlorine tablets over chlorinating in-ground-spa. Best way to chlorinate?

    FC is Free Chlorine, ie the level that matters for sanitizing. CC is Combined Chlorine, by-product from free chlorine doing its work. I believe your test measures total chlorine, ie FC + CC, which is easy to test but not as useful as the individual FC/CC levels. The standard recommendation here is to get a test kit which can measure FC and CC independently.

    Tabs add both FC and CYA -- FC gets used up but CYA accumulates and eventually causes problems. Bleach adds only FC.

    More details in Pool School => Getting Started => ABC's of Water Chemistry

    http://www.troublefreepool.com/conte...ater-chemistry

    List of recommended test kits at Pool School => Pool Chemistry => Test Kits Compared:

    http://www.troublefreepool.com/conte...its-comparison

    The Pool School pages are a really good source of info.
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    Re: Chlorine tablets over chlorinating in-ground-spa. Best way to chlorinate?

    Thanx John- Very helpful. I find acronyms confusing if I have not seen them before. I decided to call of couple test kit companies and was told that CYA stands for Cyanuric Acid a stabilizer for tablets, which is 10% of the tablets I am using.

    According to the Taylor, and Blue Devil CYA is a good thing because it lowers pH and keep the Free chlorine (FC) from destabilizing quickly. Taylor said to drain the spa every 6 months, and Blue Devil said that if you test for total hardness, you essentially do not have to test for CYA because as total hardness goes up, you will need to drain the spa and will most likely occur before the levels of CYA becomes an issue. However, I bought CYA test strips from Aqua Check for $8.00, as a precaution.

    So, according to three test kit companies, I am testing correctly with Orthotolidine. I also have total chlorine test strips for a control.

    The original question was not answered, which was; how to chlorinate correctly with a small spa and why does it only take 24 hours to over chlorinate with tablets?

    The solution is simple. First of all the cause is the fact that I now have a tiled spa compared to a concrete spa. Apparently, there is a significant difference, as I did not have an issue with the concrete spa. The tile is glass, and clearly does not required as much chlorine. Wait for it... I need to use at least 1/2 the amount of tablets in the float.

    So, dahh to me, I need to use less chlorine tablets in the Float. As you can see in the photo, I am using about 4 broken pieces of the 3" tablet, which is about 1/2 a 3" tablet. I will need to experiment, and add about 1/4 tablet or possibly 1/8 tablet in the float in order to avoid over chlorination.

    I am more knowledgeable, now that I know I am adding Cyanuric Acid, which I did not know about when I asked my question.

    Thank you again for your help/push in the right direction, as now I know what CYA is and was able to ask questions to the kit companies based on that knowledge.

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    Re: Chlorine tablets over chlorinating in-ground-spa. Best way to chlorinate?

    Yep, less surface area should reduce the rate of chlorine release. I think you want to use only one piece of whatever size gives you the correct release rate -- if you take that one piece and break it into two smaller pieces the release rate will go up.

    Just realized I didn't spell out what CYA was, thought I did. Must have accidentally nuked it with a fat-fingered copy/paste, sorry.

    As far as I know there are two major things to watch out for with trichlor in a spa. One is that it takes the pH down, so check that regularly. The other is that as CYA levels go up you'll need correspondingly higher levels of FC to achieve the same sanitizing effect -- see table at Pool School => Handy Reference -> Chlorine/CYA Chart:

    http://www.troublefreepool.com/conte...art-slam-shock

    My understanding is that CYA mostly protects the FC levels against breakdown from UV (eg sunlight), so it won't necessarily help you there unless your spa runs topless most of the time. I keep my hot tub covered when I'm not using it so the main reason for keeping a CYA level is to moderate the effects of the chlorine (with zero CYA you need to run very-low-and-difficult-to-maintain FC levels).

    I have been using what is probably still called the "dichlor/bleach method" (from years-ago posts by Chem geek), where after each fill I start sanitizing with dichlor until CYA level gets up to ~30ppm then switch to using chlorinating liquid until the next refill to keep CYA levels where I want them. Works well for me, and since you have a big pile of trichlor tabs and a good handle on controlling release rate you could probably put together a nice "trichlor-bleach" regimen instead.

    I have a bit of doubt about the "if you test TA you don't need to test CYA" advice you were given... my guess is that the trichlor will hold TA down a bit (only a guess though) so you'll need to drain because of CYA before TA. As long as you test CYA levels regularly you should be OK though. I'm probably using the same AquaCheck strips as you for daily testing -- pH, FC, TA, CYA ? -- and a Taylor K-2006 kit on the weekend to keep my eyes and the test strips honest.
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    Re: Chlorine tablets over chlorinating in-ground-spa. Best way to chlorinate?

    Thanx For the Link- that will be very useful when I get my test strips. I'll post the results tomorrow. I am now curious to see what the results will be considering how high the total amount is. However, because the CYA in the tables is only at 10%, my guess is the FC is higher.

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    Re: Chlorine tablets over chlorinating in-ground-spa. Best way to chlorinate?

    Quote Originally Posted by norwood451 View Post
    Thanx For the Link- that will be very useful when I get my test strips.
    Not likely ... test strips are not well thought here of due to their inaccuracy and inconsistency. These are the Recommended Test Kits.

    And I provided that link earlier
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    Re: Chlorine tablets over chlorinating in-ground-spa. Best way to chlorinate?

    BTW my recollection is that even if CYA is only 10% of the tablets (which doesn't sound right to me, CYA is part of trichlor itself not an additive) the ratio of CYA ppm added to FC ppm added is a lot higher than 10%.

    I think the number for trichlor is something like adding 6 ppm of CYA for every 10 ppm of FC... and of course the FC goes away while the CYA sticks around.

    EDIT - if you don't mind headaches, this seems like a decent thread :

    http://www.troublefreepool.com/threa...t-am-I-a-moron
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    Re: Chlorine tablets over chlorinating in-ground-spa. Best way to chlorinate?

    Thanx John. I am not sure if I want to spend any more money on a new kit yet. For 8 bucks I will have a general idea and I find using strips give me the same results as liquid reagents, maybe I am lucky. The water in the spa in only 4 months old and tends to evocate quick because there is a large surface area and no cover. Also, when I use the spa--not often, the water evaporates down several gallons. My guess is I have lost over 1/2 the water I put into it since I filled it. I have some chemistry background as a wine enologist, so my understand of chemistry is higher than most. Of course, wine is very different compared to pools, but the concepts are similar. With wine, you do not rely on just one type of test if the results are important, which is always the case with wine. The nice thing about a spa, is you can start over by draining. Anyway, I am not too worried about the amount of CYM is in the spa today. I might be conserved in a few months, and I might get a CYM test and compare the results with the strips then.

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    Re: Chlorine tablets over chlorinating in-ground-spa. Best way to chlorinate?

    There is also a fundamental flaw in that logic about CYA and CH build up in the advice you received from Blue Devil. CH build up will greatly depend on the CH level of your fill water and if you are adding chemicals like Cal-Hypo which will increase your CH along with your FC. The problem here is CH of fill water varies considerably depending on your location, and build up is also going to vary depending on rate of evaporation. Some parts of the U.S., most notably the southwest tends to have very high CH levels in their fill water (over 500 ppm in some places) vs other parts of the country may have much lower CH levels, here in Louisiana my fill water averages around 60 - 70 ppm CH seasonally, some board members have reported values as low as 30 ppm CH in their fill water without any hardness treatment
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    Re: Chlorine tablets over chlorinating in-ground-spa. Best way to chlorinate?

    Quote Originally Posted by norwood451 View Post
    The water in the spa in only 4 months old and tends to evocate quick because there is a large surface area and no cover. Also, when I use the spa--not often, the water evaporates down several gallons. My guess is I have lost over 1/2 the water I put into it since I filled it.
    Yeah, the complication here is that CYA doesn't evaporate so the evaporation/refill cycle doesn't bring CYA levels down. Presumably the same for total hardness. Leaks and splash-out help though... and a full drain/refill gives you a fresh start every time.

    My original plan was frequent drain/refills and not worrying so much about chemistry, but I found that drain/refill was a real pain in the middle of winter so I needed to learn how to keep water happy for a few months at least. I have a wooden tub where trichlor is verboten**, and dichlor brings the CYA levels up even faster than trichlor does so CYA accumulation to problem levels happens even faster.

    ** The concerns about trichlor and wooden tubs seem to be primarily related to too-fast release leading to too-high chlorine & too-low pH, so your "less than a tab" approach might work there as well

    Anyways, the important thing is getting the right FC level for whatever CYA level you have so that your tub stays safe and clean. We don't have the same challenges as a pool owner re: getting the right level for SLAM-ing because we can always drain and start over, so there's a good chance you'll drain & refill before CYA becomes a problem anyways, but the key message from this site is something along the lines of "understand what's going on, know what's in your water, and you're not likely to get bad surprises".
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    Re: Chlorine tablets over chlorinating in-ground-spa. Best way to chlorinate?

    John- Good point about evaporation and the CYA staying behind. Unfortunately, I have accidently overfilled my spa a couple of times-oops. Fortunately, I have a good overflow drainage system and the funny thing is it is kind of like draining, or at least similar, as I used about the same amount of water I would have if I drained off 1/3 or so of the water.


    RESULTS: 0 or under 30ppm CYM, 5ppm FC. According to Aqua Check. 5ppm is ok with a spa. However, I do not know how high the FC actually is due to the testing method.

    Conclusion: Buy a test kit that accurately determines FC at a range from 5+ppm, as the two methods I have been using only provide an value up to 5ppm.

    John- I am sure you know this, but Never let you wooden hot tub go dry. My mom did and it leaked after.

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    Re: Chlorine tablets over chlorinating in-ground-spa. Best way to chlorinate?

    Issaac- You mentioned "hardness treatment" do you know a way to reduce hardness other than draining or reverse osmosis? My hardness is the same as it was when I filled the spa @250, which I read is about right.

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    Re: Chlorine tablets over chlorinating in-ground-spa. Best way to chlorinate?

    Quote Originally Posted by norwood451 View Post
    Unfortunately, I have accidently overfilled my spa a couple of times-oops. Fortunately, I have a good overflow drainage system and the funny thing is it is kind of like draining, or at least similar, as I used about the same amount of water I would have if I drained off 1/3 or so of the water.
    Yep, that will help to keep the CYA levels under control. Good point.

    Until you get a kit that can test >5ppm FC, you can dilute your water 1:1 then double whatever the chlorine reading is (or 2 parts tap water to 1 part spa water and triple etc..).

    The thing that makes spa water management interesting is that most of your chlorine consumption will be driven by bather load (since #users relative to water volume is much higher than for a pool) rather than from loss to UV (pools get sunlight every day, spas are typically covered), so if you test right after use you'll probably find FC levels around zero, drifting up slowly as bather waste gets oxidized and more chlorine gets released by the floater.

    I guess there's an argument for using a floater with full tabs (or even broken-up tabs), tossing it in immediately after use then taking it out after the right number of hours. That would come closer to what I do with bleach, basically dumping in a dose right after use based on #bather-hours so that chlorine level jumps up immediately and goes to work on bather waste.

    With a pool there's "more water than bathers" so FC levels don't drop to zero just because someone sat in the pool for an hour
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    Re: Chlorine tablets over chlorinating in-ground-spa. Best way to chlorinate?

    Quote Originally Posted by bridgman View Post
    Yep, that will help to keep the CYA levels under control. Good point.

    Until you get a kit that can test >5ppm FC, you can dilute your water 1:1 then double whatever the chlorine reading is (or 2 parts tap water to 1 part spa water and triple etc..).

    The thing that makes spa water management interesting is that most of your chlorine consumption will be driven by bather load (since #users relative to water volume is much higher than for a pool) rather than from loss to UV (pools get sunlight every day, spas are typically covered), so if you test right after use you'll probably find FC levels around zero, drifting up slowly as bather waste gets oxidized and more chlorine gets released by the floater.

    I guess there's an argument for using a floater with full tabs (or even broken-up tabs), tossing it in immediately after use then taking it out after the right number of hours. That would come closer to what I do with bleach, basically dumping in a dose right after use based on #bather-hours so that chlorine level jumps up immediately and goes to work on bather waste.

    With a pool there's "more water than bathers" so FC levels don't drop to zero just because someone sat in the pool for an hour
    Thanx John- I tried your dilute method and it did the trick. I also like you idea about adding bleach after using the spa, as that is the time the levels are at it's lowest. However, after reading this forum, you have to wonder if it would not be better you just put the float into the spa so you get the added benefit of the stabilizer. I guess it would cost less for the chemicals, but not sure if a significant savings. In my case, since we do not use the spa much and the fact that I get over-chlorination in a short time after adding the float, it may make more sense to use the float. However, your point is well taken, you have to roll with the punches and adjust according to the usage, which has certainly made me reevaluate my methodology.

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    Re: Chlorine tablets over chlorinating in-ground-spa. Best way to chlorinate?

    CYA buildup in the spa is the same issue as with pools so you can't use a floater for very long. For spas, a CYA level of around 30-40 ppm works well. With hot spa temperatures, the CYA may drop by around 5 ppm per month since it does slowly get oxidized by chlorine. The approach we usually recommend is the Dichlor-then-bleach method where Dichlor is used initially as your chlorine source until the CYA builds up and then one switches to using bleach. One doses after the soak with an amount such that they start off with 1-2 ppm FC for their next soak. That minimizes chloramines during the soak while handling the bather load immediately after the soak.
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    Re: Chlorine tablets over chlorinating in-ground-spa. Best way to chlorinate?

    Quote Originally Posted by chem geek View Post
    CYA buildup in the spa is the same issue as with pools so you can't use a floater for very long. For spas, a CYA level of around 30-40 ppm works well. With hot spa temperatures, the CYA may drop by around 5 ppm per month since it does slowly get oxidized by chlorine. The approach we usually recommend is the Dichlor-then-bleach method where Dichlor is used initially as your chlorine source until the CYA builds up and then one switches to using bleach. One doses after the soak with an amount such that they start off with 1-2 ppm FC for their next soak. That minimizes chloramines during the soak while handling the bather load immediately after the soak.
    Thank you for that. unfortunately I purchased 60lbs of 3" chlorine tablets.. Until you mentioned it, I never heard of Dichor. So, another sanitizing method would be expensive as I would need toss away the 60 lbs of tabs. However, after I run out of 3" tabs, which will be a while I will certainly consider alternatives.

    However, I researched Dichor and noticed that the cost can be 2-3 times the cost of 3" chlorine tablets. I am guessing to would not be relevant, as the use of Dichor would be temporary, so a small amount would be needed for startup and a Free chlorine (FC) source (bleach) would be the primary sanitizer?

    I am understanding the method correctly? Do you switch to bleach and never use Dichor again, as you stated "one switches to using bleach"
    Also, would it make sense to add a liquid or powder stabilizer, such as Cyanuric Acid (CYA) with bleach instead of Dichor? I would think with liquid or powder, you would have more control. However, it may not be cost effective, but I guess that would depend on how much would be needed, as the cost is about $5 pre pound. I did see a product called Instant Pool Conditioner for $33 gal, but if you only use a 1/8 cup it is not that expensive.

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    Re: Chlorine tablets over chlorinating in-ground-spa. Best way to chlorinate?

    Once you add the CYA with the dichlor then you use bleach. But, the CYA will slowly drop requiring more dichlor eventually and then any time you drain the tub.

    Dichlor is very similar to the trichlor tablets you have it just dissolves faster and has a different amount of CYA in it. You could do a "Trichlor then bleach" method in the exact same way.
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    Re: Chlorine tablets over chlorinating in-ground-spa. Best way to chlorinate?

    Just keep in mind that if you use Trichlor that it is quite acidic so will lower pH and TA. So with the Trichlor then bleach method, you wouldn't lower the TA initially and instead would let the Trichlor do that for you. Since for every 10 ppm FC added by Trichlor it will increase the CYA by 6 ppm and lower the TA by 7 ppm when the chlorine gets used/consumed, you'd want your initial TA to be around 90-100 ppm when you start out. Then after using Trichlor to get to 30-40 ppm CYA (so after adding around 50-65 ppm FC cumulatively added), your TA will be down to around 50 ppm which is where you want it when you switch to using bleach.

    Also note that Trichlor dissolves faster in hot water so you'd need a special dispenser you can turn way down to slow the dissolving rate. Be sure the dispenser open at the bottom and is solid at the top.
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