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Thread: Using Trichloro tablets ocassionally to maintain CYA level

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    Using Trichloro tablets ocassionally to maintain CYA level

    I have a 12,000 gallon plastered gunite pool that I've been maintaining almost exclusively with 11% liquid bleach for about a year now. After recovering from excessive CYA last year I'm very careful of monitoring and maintaining my CYA levels. I try to keep CYA at about 30, I haven't had a problem with it drifting lower but I can only measure it down to about 25-30 with the Taylor kit and I want to know just what it is.

    The CYA level drops very slowly due to normal water losses so I must bolster it occasionally. I have some Clorox Active 99 3" Trichloro tablets I'd like to use-up and figure using them to bolster CYA may be their best use. My question is how to judge how effective they'd be at that role and how to judge how many to use for a particular adjustment. I found a thread on TFP where someone with a 12,000 gallon pool found an increase in CYA of 30 by using only a total of 5 pucks. That translates to an increase of 6 CYA per puck. That seems like a lot. Does that seem reasonable and if not can someone give me an idea of what to expect?
    Gunite free-form pool in Port Orange Florida with original white plaster lining. Capacity about 12,000 gallons. Pool age about 18 years and fully enclosed by screen room. Using liquid chlorine bleach (10%) dispensed by hand. Taylor K-2006 test kit.

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    Mod Squad mknauss's Avatar
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    Re: Using Trichloro tablets ocassionally to maintain CYA level

    Use Effects of Adding Chemicals in PoolMath. You input your pool volume in the upper left and then down towards the bottom of the page you put in what you are adding and it will tell you the effects to the water chemistry.

    For example, in your 12000 gallon pool, an 8OZ trichlor tablet will raise your water FC by 4.6ppm, your CYA by 2.8ppm, lower your pH by 0.24, and raise your salt by 3.7ppm
    6000 Gallon IG Fiberglass with integrated Spa;Pentair CCP240 Cartridge Filter with Pentair Intelliflo VS Pump and HTR250 heater. IC40 SWG. EasyTouch 4. Dolphin Active20 Robot "Roadrunner", TF 100 Test Kit w/SpeedStir!
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    Marty

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    JoyfulNoise's Avatar
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    Re: Using Trichloro tablets ocassionally to maintain CYA level

    As Marty said, the Effects of Adding Chemicals section in Pool Math can help you out. Most 3" trichlor pucks are about 8oz, give or take. Don't pay much attention to the pH changes as those are only very rough estimates and assumptions are being made about the TA of the water. As long as you have sufficient alkalinity in the pool water, the pH decrease from dissolving trichlor pucks will be unnoticeable. Just keep an eye on your TA and adjust as necessary.

    The only downside to using pucks is this - they are very slow to dissolve (that's a feature, not a bug). So if you were looking to raise CYA quickly, then pucks are not the best method. Dichlor powder dissolves more quickly than trichlor and is less acidic (it also raises the FC by less).
    Matt
    16k IG PebbleTec pool, 650gal spa, spillway and waterfall, 3HP IntelliFlo VS / 1.5HP WhisperFlo, Pentair QuadDE-100 filter, IC40 SWCG, MasterTemp 400k BTU/hr NG heater, KreepyKrauly suction-side cleaner Dolphin S300i robot, EasyTouch controls, city water, K-1001, K-2006 and K-1766 test kits, Mannitol test for borates

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    Re: Using Trichloro tablets ocassionally to maintain CYA level

    Thanks for the advice and guidance. I had no idea that the "effects" portion of the pool math existed. A very valuable reference I'll start using immediately.

    The predicted FC increase of 4.6 looks suspicious to me however. I'm assuming that would assume no FC loss and the tablets take many days to dissolve. Can I assume if the rate of FC loss is normally about .7 per day then adding a Trichlor tablet will hold FC constant for about a week that it takes to dissolve?
    Gunite free-form pool in Port Orange Florida with original white plaster lining. Capacity about 12,000 gallons. Pool age about 18 years and fully enclosed by screen room. Using liquid chlorine bleach (10%) dispensed by hand. Taylor K-2006 test kit.

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    Re: Using Trichloro tablets ocassionally to maintain CYA level

    FC loss per day in a healthy pool with no swimmers that's at swimmable temperature is usually 2-4ppm depending on sun strength and a few other factors. Colder water will lower the FC loss.

    Start with one tab and test the following day to see where you are. Add a second if it's not keeping up, but do carefully watch that CYA level.
    8,500gal plaster in-ground with attached spa, two floor drains, one skimmer. Chlorine, City Water.
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    Re: Using Trichloro tablets ocassionally to maintain CYA level

    Lately my pool is dropping only 1 ppm FC or less per day when trying to maintain it at about 4 ppm with CYA at about 25 and water temp about 70. Perhaps the full screen enclosure is partially why it drops so little this time of the year.

    I added one tab last week when the FC measured 5.0. I checked it again 48 hours later and measured the same 5.0 FC. The tab hardly changed in size in those two days so I suspect it will last a full week and perhaps keep the FC fairly constant for that week. Unfortunately I had to leave town three days after adding the tab and I'll likely be away for a few weeks so I won't be able to observe the tab dissolving or measure the CYA directly afterwards. I'll keep in touch with my "pool caretaker" while I'm away and play it by ear.

    It sounds like 3-4 tabs will get me back to about 35 CYA. The pool seems fine and doesn't use excessive amounts of chlorine even with 25 CYA so I'm not in a hurry to raise it. I'll check CYA level when I return and use the tabs sparingly when the pool has less attention and using the tabs will be an advantage.
    Gunite free-form pool in Port Orange Florida with original white plaster lining. Capacity about 12,000 gallons. Pool age about 18 years and fully enclosed by screen room. Using liquid chlorine bleach (10%) dispensed by hand. Taylor K-2006 test kit.

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    Re: Using Trichloro tablets ocassionally to maintain CYA level

    Sounds like you're on top of it! Feel free to ask any other questions you may have in this thread as time goes on.
    8,500gal plaster in-ground with attached spa, two floor drains, one skimmer. Chlorine, City Water.
    Pentair WhisperFlo 1hp Pump, MagnaTek Midcentury EPlus motor, Pentair CleanNClear 200SF Cartridge filter, Purex Triton MiniMax 250 Gas Heater, Pentair SunLite, AutoFill.
    Kreepy Krauly Cruiser, TF-100 with SpeedStir. :D

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