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Thread: How much CYA do trichlor tablets add?

  1. #1
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    How much CYA do trichlor tablets add?

    Hi all,

    After topping off the pool (we had closed it for the winter) and some spring rains, my CYA level has dropped to 10 ppm or less.

    I have a leftover bucket of HTH trichlor tabs from the previous owner.

    Does anyone have an approximation of how much CYA is added over time by the tabs?

    I'm thinking I could just use the tabs until my CYA gets back up to 40-50 before going back to BBB. Being cheap , I'd also like to save on the CYA test reagent by not testing more frequently than I need to.

    If this is a stupid idea and I'd be better served by buying some stabilizer at the pool store, feel free to tell me so.

    Thanks,
    Julian
    13K gal - IG gunite/plaster - 1 1/2 HP pump - 300lb. sand filter - SWCG
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  2. #2
    Administrator JasonLion's Avatar
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    Re: How much CYA do trichlor tablets add?

    In 13,000 gallons, 10 lbs of trichlor will raise the CYA level by 50. You can use my Pool Calculator, see the link in my signature, to make this kind of calculation. See the Effects of adding chemicals section near the bottom.

    One of the problems with using trichlor right now is that the CYA level comes up fairly slowly. For a while at first your CYA level will be too low.

    I would save the trichlor for use when you are on vacation.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
    TFP Admin. Creator of PoolMath and Pool Calculator. Other handy links: Support this site, TF Test Kits, Pool School

  3. #3
    Senior Member AV8TOR's Avatar
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    Re: How much CYA do trichlor tablets add?

    Quote Originally Posted by JasonLion

    I would save the trichlor for use when you are on vacation.
    Just what I have been pondering as I have a 2-week Asia trip coming up next month. How many pucks should I load in the feeder for 2-weeks? I have been BBB since we bought our house last November. After a 50% partial drain to get the CYA down I hate like heck to use the tabs though but for the convenience I am thinking about it.
    Double Roman Gunite In ground Pool
    Aquatech NS/FNS-48 7lb DE filter w/2-skimmers
    Polaris 280
    BBB along with Borates
    TF100

  4. #4
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    Re: How much CYA do trichlor tablets add?

    I have a couple trips coming up too, so I will take a crack at this.

    Last winter (pre-TFP) I was trying to keep about 3 pucks worth in the floater, and it seems I was adding maybe 1 puck/week with the water temp probably around 50. Pucks will dissolve faster in warmer water, but no worthwhile data there. This means we get to assume optimal conditions!

    The trusty Pool Calculator says each 8-oz puck is worth 4.1ppm FC in a 13,500 gal pool. For simplicity assume a puck lasts the whole 2 weeks, and call it 4.2ppm, so each puck is worth about .3ppm FC per day. Figure out how much you lose normally, and use enough pucks to make up the difference. If you lose 1ppm/day then you'd want 3-4 pucks. (Each puck will also add about 2.5ppm CYA.)

    Does that sound reasonable?
    --paulr
    BBB "Intermediate Swimmer"
    IG plaster pool 18.5K gal, Hayward Pro-Grid DE filter, 3/4 HP Hydramax II; Polaris 380, 3/4 HP booster
    AG spa 325 gal, probably Sundance of some kind
    Water testing instructions on one page

  5. #5
    Senior Member AV8TOR's Avatar
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    Re: How much CYA do trichlor tablets add?

    Quote Originally Posted by PaulR
    Does that sound reasonable?
    --paulr
    Sounds good Paul. I did not know the weight of the pucks thanks.

    In doing some searching I see some people do a shock before they leave. Is it safe to say then that if you shock to 20 ppm and you loose 1 ppm/day there will be 4 ppm left after 16 days? I have been experimenting with a drip system similar to what I use in my Coral Aquariums dripping Kalkwasser. In counting drops/minute is is pretty easy to calculate ounces added/day. I hate the thought of adding any CYA after my last 50% drain so I am thinking of Shocking to 20 ppm and doing a drip from a 2-1/2 gallon container. I am not leaving for 2 months so I am doing some drip experimenting in the pool now.
    Double Roman Gunite In ground Pool
    Aquatech NS/FNS-48 7lb DE filter w/2-skimmers
    Polaris 280
    BBB along with Borates
    TF100

  6. #6
    Administrator JasonLion's Avatar
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    Re: How much CYA do trichlor tablets add?

    The amount of chlorine you lose each day will be a percentage of the amount you start with, not a uniform amount. If you start at shock level, you will lose the most on the first day and less each subsequent day.

    Your drip feeder can still work, just adjust it for your routine chlorine loss, and don't worry about the higher loss after shocking.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
    TFP Admin. Creator of PoolMath and Pool Calculator. Other handy links: Support this site, TF Test Kits, Pool School

  7. #7
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    Re: How much CYA do trichlor tablets add?

    Quote Originally Posted by JasonLion
    The amount of chlorine you lose each day will be a percentage of the amount you start with, not a uniform amount.
    Yes, I should have stated it in terms of how much you typically add, rather than lose. And of course if you maintain a fairly uniform level, then what you lose each day will also turn out to be fairly uniform; but thinking in terms of percentages will be more accurate.
    --paulr
    BBB "Intermediate Swimmer"
    IG plaster pool 18.5K gal, Hayward Pro-Grid DE filter, 3/4 HP Hydramax II; Polaris 380, 3/4 HP booster
    AG spa 325 gal, probably Sundance of some kind
    Water testing instructions on one page

  8. #8
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    Re: How much CYA do trichlor tablets add?

    I have been experimenting with a drip system similar to what I use in my Coral Aquariums dripping Kalkwasser. In counting drops/minute is is pretty easy to calculate ounces added/day. I hate the thought of adding any CYA after my last 50% drain so I am thinking of Shocking to 20 ppm and doing a drip from a 2-1/2 gallon container. I am not leaving for 2 months so I am doing some drip experimenting in the pool now.
    Tel us more. I have home-brewed a couple of chlorine delivering devices.....none worked well. The drip idea is encouraging but what do you use to control the drip? How do you prevent crystallization at the drip point? What do you drip into?
    Dave S.
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  9. #9
    Senior Member AV8TOR's Avatar
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    Re: How much CYA do trichlor tablets add?

    Quote Originally Posted by duraleigh
    I have home-brewed a couple of chlorine delivering devices.....none worked well. The drip idea is encouraging but what do you use to control the drip? How do you prevent crystallization at the drip point? What do you drip into?
    What I have done for years with my calcium dosing in my aquariums is use a high quality aquarium air regulator (needle valve). Right now as a test I am using a cheep one and it still looks like it is working fine. Right now I am using a empty Bleach bottle but I will use a 2-1/2 gallon water bottle. Get some silicone airline tubing and puncture a hole with an Al and quickly push in the silicone tube in. I say quickly because if done right the bottle will slowly collapse against the tubing making a leak proof connection. Attach the air regulator and adjust it for around 25 drops/min. In a day it will reduce to around 15 drops and stay there. I have been dosing bleach for a week right now as a test and it has not slowed down from there. For those that want to calculate 600 drops = 1 oz. It may not be super precise as a commercial dosing system but it is putting chlorine into your pool. I just have the bottle on the edge of the pool dripping into the pool 24/7. I am not looking for something to do this all season long just while I am away. I have not seen any signs of crystallization but then again it has only been a week. There are some really nice brass valves if I can find some locally. Still working on it.

    Double Roman Gunite In ground Pool
    Aquatech NS/FNS-48 7lb DE filter w/2-skimmers
    Polaris 280
    BBB along with Borates
    TF100

  10. #10
    Senior Member Gooserider's Avatar
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    Re: How much CYA do trichlor tablets add?

    I could be way off base, but seems to me like you might actually be better off with a plastic valve than a brass one... Chlorine is a fairly active and nasty reagent that attacks all sorts of stuff. I wouldn't be at all surprised to see it do a real number on brass, while most plastics don't seem to be bothered by it.

    I know that it seems pool equipment makers try really hard to keep metals out of the system, and when they do use them, it seems to be mostly stainless. I know that on our pool, the only brass that I'm aware of is the tee fitting for the pressure gage and air vent on top of the filter...

    Gooserider
    Free-form Inground gunnite pool, Estimated 16-17K gallons. New Pentair TR60 ClearPro 24" sand filter and Compupool CPSC-48 SWG, Hayward Mod SP1607X10 Pump w/ 1HP replacement motor, 1.5" plumbing all over, Polaris Pressure side cleaner w/ booster pump, pool is more than 20 yrs old, less than 35. Not painted, deteriorating tile surround.

    I am paraplegic, get in/out of pool w/ S.R. SMITH PAL portable pool lift (significantly modified)

    Sand filter replaced aged Purex DE filter that was hard to maintain.

  11. #11
    Member schrody's Avatar
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    Re: How much CYA do trichlor tablets add?

    I'm in a similar situation where my CYA is low and I have a ton of tabs. I noticed someone mentioned 8 oz per tab...is that for the 1" variety? Anyone know the approximate weight of 3" tabs?

    I also like the idea of using them for a little while to keep the pH low so I can slowly add some more borates. I know this isn't the optimal method but it looks to be the cheapest for now.
    12,000 gallons - IG - Vinyl
    IntelliFlo VF Pump
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  12. #12
    Administrator JasonLion's Avatar
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    Re: How much CYA do trichlor tablets add?

    The larger 3" tabs are 8 oz. There are also slightly smaller 3" tabs that are 7 oz.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
    TFP Admin. Creator of PoolMath and Pool Calculator. Other handy links: Support this site, TF Test Kits, Pool School

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