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Thread: CYA reduction by water evaporation

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    CYA reduction by water evaporation

    Hello all. Recently dumped my pool service and their pucks and started using liquid chlorine only. My CYA is 60 which forces me to have my FC at 7. My question is, I live in a hot desert climate with high temps and low humidity which leads to a fair amount of evaporation. I can lose 1/2" to 3/4" of water on some really hot days. Over time, will my CYA level drop due to adding water to my pool every couple of days? I live in CA, so draining is not an option.
    38000 Gal, IG, Plaster, 20' x 40' x 10', Attached Raised Spa, Intelliflo VS 3 HP (011018), Pentair Quad DE 60 Filter, Raypak (Rheem) 400,000 BTU (407a low Nox), Easy Touch 8 upgrade, Screenlogic 2 with wireless, IS-4 Spa Side Remote, Stenner 45MPHP10 w/15 gal tank, Intellibrite 5g (3), Dolphin Triton Plus robot with PRO remote, Water Tech Catfish handheld vacuum for spa, TF100 with SpeedStir.

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    Texas Splash's Avatar
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    Re: CYA reduction by water evaporation

    Hello! Here's a neat thread on that very question: CYA Level and Evaporation
    Pat (a.k.a. Texas Splash) ~ My Pool: Viking Fiberglass; 17,888 Gal; Waterway Supreme 2-sp/2-hp pump; Hayward Ctg filter; TF-100 w/ Speed Stir
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    Re: CYA reduction by water evaporation

    I would not be too quick on trying to lower the CYA for your climate. See how much chlorine you are using to get an idea if that level of CYA is helping or not.

    You might want to install a Pentair IC60 SWG as that would fit in nicely with your pool.
    16k gal plaster with raised spa, Jandy DEV60 filter, 2 HP 2-speed SHPF Jandy Stealth pump
    Hayward Aqua Rite T-15 SWCG, Jandy LXi 400k BTU NG heater, 350 sq.ft. of Sun Star solar panels, TF-100 Test Kit, Dolphin s300i Cleaner
    Test Kits . Pool Math . Chlorine/CYA Chart . The SLAM Process

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    Re: CYA reduction by water evaporation

    You could consider using a pool cover to eliminate evaporation and since I presume you don't need any solar heating, you can use a white or reflective opaque cover. That will prevent heating of the pool and will also cut down on chlorine breakdown from sunlight.
    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
    12 Fafco solar panels; Purex Triton PowerMax 250 natural gas heater (200,000 BTU/hr output); automatic electric pool safety cover; 4-wheel pressure-side "The Pool Cleaner"

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    Re: CYA reduction by water evaporation

    For various reasons, I do not want a cover. The SWG might be a consideration, however. My existing CYA would be in the range for a SWG. Is the IC60 the best choice given my pool size (38,000 gal) and using an Easy Touch 8 controller?
    38000 Gal, IG, Plaster, 20' x 40' x 10', Attached Raised Spa, Intelliflo VS 3 HP (011018), Pentair Quad DE 60 Filter, Raypak (Rheem) 400,000 BTU (407a low Nox), Easy Touch 8 upgrade, Screenlogic 2 with wireless, IS-4 Spa Side Remote, Stenner 45MPHP10 w/15 gal tank, Intellibrite 5g (3), Dolphin Triton Plus robot with PRO remote, Water Tech Catfish handheld vacuum for spa, TF100 with SpeedStir.

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    Re: CYA reduction by water evaporation

    As shown in this thread, the IC60 is the most economical and in your case with your larger pool it's essential for you to get this largest unit. It outputs 2 pounds of chlorine every 24 hours. Type the following into Google search:

    2 pounds per 24 hours per 38000 gallons in milligrams per liter per hour
    and you will get

    0.262777253 (milligrams per liter) per hour
    so 0.26 ppm FC per hour from the IC60 in your pool when it is on (at 100% ontime). With your hot climate, you'd probably want your CYA even higher at 80 ppm after you get the SWCG. As shown in this post, the FC loss per hour at 80 ppm CYA with 4 ppm FC might be around 0.12 ppm though this varies by pool, but your SWCG should be able to keep up without a problem. In theory, you may be able to run with 0.12/0.26 = 46% ontime during the peak daylight hours, but you'll just need to adjust this until it works well for your pool so that you still have at least 4 ppm FC when the SWCG turns on at the start of a day.

    The bigger concern regarding the evaporation is not just the water waste but the refill with water that the 2014 Riverside Water Quality Report shows Total Hardness at 208 ppm and since Calcium Hardness (CH) is typically 70% of Total Hardness, that would make CH at around 145 ppm so actually not so bad. As shown in this pan evaporation list, Riverside in May through September averages 9" per month or 0.3" per day evaporation. If you have a 6' deep end and a 3' shallow end so average pool depth of 4.5', then your CH will increase by 145*((9/12)/4.5) = 24 ppm per month so over 6 months that's 145 ppm. So long as you dilute some with winter rain overflow each year, you should be OK.
    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
    12 Fafco solar panels; Purex Triton PowerMax 250 natural gas heater (200,000 BTU/hr output); automatic electric pool safety cover; 4-wheel pressure-side "The Pool Cleaner"

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    Re: CYA reduction by water evaporation

    Quote Originally Posted by chem geek View Post
    As shown in this thread, the IC60 is the most economical and in your case with your larger pool it's essential for you to get this largest unit. It outputs 2 pounds of chlorine every 24 hours. Type the following into Google search:



    and you will get



    so 0.26 ppm FC per hour from the IC60 in your pool when it is on (at 100% ontime). With your hot climate, you'd probably want your CYA even higher at 80 ppm after you get the SWCG. As shown in this post, the FC loss per hour at 80 ppm CYA with 4 ppm FC might be around 0.12 ppm though this varies by pool, but your SWCG should be able to keep up without a problem. In theory, you may be able to run with 0.12/0.26 = 46% ontime during the peak daylight hours, but you'll just need to adjust this until it works well for your pool so that you still have at least 4 ppm FC when the SWCG turns on at the start of a day.

    The bigger concern regarding the evaporation is not just the water waste but the refill with water that the 2014 Riverside Water Quality Report shows Total Hardness at 208 ppm and since Calcium Hardness (CH) is typically 70% of Total Hardness, that would make CH at around 145 ppm so actually not so bad. As shown in this pan evaporation list, Riverside in May through September averages 9" per month or 0.3" per day evaporation. If you have a 6' deep end and a 3' shallow end so average pool depth of 4.5', then your CH will increase by 145*((9/12)/4.5) = 24 ppm per month so over 6 months that's 145 ppm. So long as you dilute some with winter rain overflow each year, you should be OK.
    **Whew** that is lot of information to digest, and I appreciate it. Looks like the IC60 is the way to go. Hopefully this winter will provide some rainwater to dilute, so fingers crossed.
    38000 Gal, IG, Plaster, 20' x 40' x 10', Attached Raised Spa, Intelliflo VS 3 HP (011018), Pentair Quad DE 60 Filter, Raypak (Rheem) 400,000 BTU (407a low Nox), Easy Touch 8 upgrade, Screenlogic 2 with wireless, IS-4 Spa Side Remote, Stenner 45MPHP10 w/15 gal tank, Intellibrite 5g (3), Dolphin Triton Plus robot with PRO remote, Water Tech Catfish handheld vacuum for spa, TF100 with SpeedStir.

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    Richard320's Avatar
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    Re: CYA reduction by water evaporation

    60 CYA is easily managed. You may actually find the daily FC losses to be less than they would be at 40 or 50 CYA. You've got a huge pool, so even with perfectly balanced chemistry, it's going to take a lot of anything to maintain FC.

    You should be grateful you weren't left with triple digit CYA. I started out in the 220-240 range - and water restrictions were in place then, too.
    16K freeform gunite with spa; Pentair 4000 DE filter; Century Whisperflow 1 HP; Pentair Minimax heater.
    Troublefree does not mean Maintenancefree. It's like brushing your teeth: You can spend a couple minutes a day and pennies a week or go to the dentist once a year and spend several thousand dollars.
    A pool is like a pet - you have to feed it every day, even the days you don't want to play with it!

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