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Thread: best method for regular chlorine dosage

  1. Back To Top    #1

    Join Date
    Jul 2016
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    Question best method for regular chlorine dosage

    I recently drained and refilled my 16000 gal outdoor (inground, gunite/plaster) pool, due to high CYA (300 ppm), high TDS (3700) and high phosphates (600). Immediately after refilling, my TDS is now 450, and phosphates is 0. My CH level is now 210. After refilling, I added enough CYA to get a starting level of 30 ppm.


    After refilling the pool, I stopped using the tri-chlor tabs in my feeder, to avoid CYA buildup, and started using liquid chlorine (10%) for regular dosing, and find that I have to add the equivalent of 2 ppm (for my pool) almost every day.


    I see that the super-chlorination shock value for my CYA level is 12 ppm of chlorine. For my pool that requires 1.8 gal of liquid chlorine, or $9.40 per shock treatment (at Leslies prices). As an alternative, i started using Leslies Fresh N clear (potassium peroxymonosulfate 38%). Their recommended regular dosage for my pool is 1.6 lbs, which costs me $6.70, based on their price for a 25 lb bucket. So it seems that the non-chlorine shock costs less, and swimming can resume much more quickly.


    1. My first question is whether using this non-chlorine shock on a regular basis is as effective as doing the super-chlorination shock? We don't swim everyday, so we can tolerate waiting a few days for high chlorine levels to subside. We usually have swimmers no more than 2-3 days a week in summer.


    2. My second question is what is the best way for me to do regular chlorination? I wanted to avoid the tri-chlor tabs, and just use them for short periods when we are away on vacation and there is no one to do daily testing and chemical maintenance. For the same reasons, I don't want to use di-chlor powder on a regular basis. That leaves me with the choice of liquid chlorine or calcium hypochlorite. The guy at the pool store said regular use of liquid chlorine will cause an excessive buildup of TDS. He said it would be better for me to use calcium hypochlorite. (The only solid I can think of from the liquid chlorine would be sodium - does that count as part of TDS?) When I told him I thought regular use of Calcium hypo would cause excessive buildup of calcium, he said that would not be a problem and could be mitigated by adding something to keep the calcium from forming scale. He said the TDS from bleach would be a problem. I don't necessarily believe anything they tell me at a pool store, So what is better: using something that increases calcium or something that possibly increases my sodium or TDS?


    Because my free chlorine levels fluctuate so fast, requiring me to tend to the pool every day, I find that I can add enough to get a FC ppm of 2 late in the afternoon, and then less than 24 hours later it is almost 0. So even if I tend to it every day (sometimes several times in a day) I can hardly keep up with the chlorine dissipation. I'm almost tempted to go back to the automatic tab feeder method, and just accept the fact that I will have to drain the pool in less than a year due to high CYA. The cost to refill the pool can be less than the cost of a lot of chemicals, but I hate to contribute to the water shortage problems in our drought area.


    On one of the TFP forums I read that, for each 1 ppm of chorine that is added from tabs, there will be 0.6 ppm of CYA added, so it won't take long before I have to drain it again if I do this. I have read the info on TFP about the required FC levels being proportional to the CYA, so I realize I'd need to monitor my CYA and increase my chlorine dosage accordingly.
    16,000 gallon outdoor in-ground 16'x32' plaster pool (built 2002); Pentair Intelliflo VF pump; Jandy Cartridge filter;Rainbow in-line chlorinator (used only when I am away); Hayward 2 wheel suction-side pool cleaner; LARS gas heater, Taylor K-2006 FAS-DPD test kit

  2. Back To Top    #2
    Mod Squad jblizzle's Avatar
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    Re: best method for regular chlorine dosage

    Welcome to TFP!!!

    Sounds like you have some of the fundamentals of TFP, but missing a few details.

    - It is normal to have to add 2-4ppm of FC to your pool every day.
    - There is NEVER a need to "shock" your pool on some schedule if you maintain the proper FC levels for your CYA. If a problem develops (and for many/most of TFPer, a problem never starts), then you follow the ShockLevelAndMAINTAIN Process to fix it.

    So the above info may invalidate some of your further questions. But I will address them.

    1. There is not a need to "shock" the pool. Just add the required FC daily to keep the FC above the minimum for your CYA level (according to the FC/CYA Chart) at all times.

    2. The pool guy has NO!!! idea what he is talking about. We ignore TDS and focus on things that matter. I would avoid the cal-hypo because that is adding calcium which will naturally rise just from evaporation. You do not want to have to replace all the water again too soon. Just stick with liquid chlorine / bleach. All the bleach adds is a little salt and this is much more tolerable than adding calcium. Basically, never go back and talk to that pool store

    You can NOT!!! let the FC drop near 0. If your CYA is 30ppm, then you should never let the FC get below 2ppm. Which means every day you should likely be raising the FC up to around 5ppm so that it is still more than 2ppm the next day. You will actually have to add less FC daily if you were to raise the CYA up to around 50ppm and keep the FC above 4ppm at all times (target 7ppm daily).
    Jason, TFP Moderator
    18k IG pebblesheen pool, Hayward ProLogic P4 w/ T-15 SWG, Pentair 1HP 2-speed Superflo, Hayward 6020 DE filter
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    Mod Squad pooldv's Avatar
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    Re: best method for regular chlorine dosage

    Welcome to TFP!

    Nice work so far! Here is some more stuff to read in Pool School.
    ABCs of Pool Water Chemistry
    Pool School - Getting Started
    Pool School - How to Chlorinate Your Pool
    TFP Moderator
    If TFP helped you or saved you money - Become a TFP Supporter! <--Click here
    2012 build and pics, 20k gal gunite, black onyx pebblesheen, OK flagstone, IntellifoVS, cart filter w/Pleatco, IC40 SWG, Solartouch, 5 12'x4' solar panels, HP50HA heat pump, 8mil solar cover, borates, TF-100 test kit, SONOS, Doheny's Discovery Robot, hot tub on bleach

  4. Back To Top    #4

    Join Date
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    Re: best method for regular chlorine dosage

    Thanks. I still do go to that pool store for supplies, but I do my own testing (including CYA testing), and am skeptical of any advice they may give. Thanks for confirming the guy didn't know what he was talking about, regarding cal-hypo vs. bleach. I've also ordered a FAS-DPD kit to get more accurate chlorine readings.
    I thought that when FC reacts with organic waste (from swimmers, leaves that blow into pool etc.), it formed chloramines, which I think is CC (combined chlorine), and that you had to superchlorinate the pool (or use some non-chlorine shock) to burn off the chloramines. I can understand there is no need to ever shock the pool if FC is high enough, and no one swims in the pool and no organic debris blows in, but what makes the chloramines go away if you don't shock it? My procedure for many years was to superchlorinate the pool from time to time during swimming season but not so much in the cooler months when no one was using the pool, because I had heard that was the only way to get rid of the chloramines formed from swimming activity.
    16,000 gallon outdoor in-ground 16'x32' plaster pool (built 2002); Pentair Intelliflo VF pump; Jandy Cartridge filter;Rainbow in-line chlorinator (used only when I am away); Hayward 2 wheel suction-side pool cleaner; LARS gas heater, Taylor K-2006 FAS-DPD test kit

  5. Back To Top    #5
    Mod Squad jblizzle's Avatar
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    Re: best method for regular chlorine dosage

    FC and the sun break down the CC.

    There is no need to "superchlorinate" on a schedule if you always maintain the proper FC level for your CYA level.
    Jason, TFP Moderator
    18k IG pebblesheen pool, Hayward ProLogic P4 w/ T-15 SWG, Pentair 1HP 2-speed Superflo, Hayward 6020 DE filter
    500 sqft Heliocol solar panels, ThePoolCleaner, TF-100 test kit w/ SpeedStir
    Pool School + Test Kit + PoolMath = A TROUBLE FREE POOL
    If you found TFP helpful and we saved you money ... Become a TFP Supporter!

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