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Thread: Understanding SWG Output levels

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    Understanding SWG Output levels

    Hi,
    I think I've seen this posted before, however I can't find it when I need it. Can anyone help with the 'base line' amount of FC a pound of chlorine should add to say 10,000 gallons of water for a given SWG? I know there are many other factors with the water chemistry and how it impacts FC levels and what the cell is doing, etc. Right now I'm trying to find the 'all other factors being the same' answer to work through some troubleshooting.
    Appx. 39,000 gal., in-ground plaster. 48 SqFt Pentair DE grid filter, 1 HP Pentair single speed pump, Circupool RJ-60+ SWG (seen here). Currently using Cellulose instead of DE. Hayward XL suction sweep. TF-100.

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    Mod Squad YippeeSkippy's Avatar
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    Re: Understanding SWG Output levels

    We need to know what your CYA level is, then we'll know what you should strive for. See this--> FC/CYA Chart

    And you can use PoolMath up at the top to tell you exactly how many ounces that you need of bleach to get your pool up to goal level, then you just need to dial in your SWG % along with how long it wll run. The important thing to know is that the SWG works best to maintain your desired level of FC, but it's too slow to bring it up to that before algae could take hold. Use bleach at first.
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    Mod Squad pooldv's Avatar
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    Re: Understanding SWG Output levels

    Enter pool gallons at the top of Poolmath and scroll down to Effects of Adding Chemicals, enter measure and select chlorine gas. It will tell you haw many ppm of FC.
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    Re: Understanding SWG Output levels

    Thanks guys. Let me redirect a little bit. I'm not looking for tips on how to tune my SWG. I'm actually helping a friend and we are trying to troubleshoot/determine if his SWG is working correctly. So let me rephrase the question a bit.

    We have a SWG that is rated for .72 LBS per day and a 10,000 gallon pool. CYA is 80. Should this SWG be able to maintain the needed 4-6 FC? It's being run >8 hrs per day on 100% and can't hold a level. i.e. FC falls no matter where it started.

    I tested his water and all other chemistry is good. I didn't write down the numbers but they were all within recommended levels. Equipment is all new. Plaster is new... about 2-3 months under water.

    This is the SWG:
    Wave 20 salt chlorine generat

    I think its a discontinued model. But newly installed.
    Appx. 39,000 gal., in-ground plaster. 48 SqFt Pentair DE grid filter, 1 HP Pentair single speed pump, Circupool RJ-60+ SWG (seen here). Currently using Cellulose instead of DE. Hayward XL suction sweep. TF-100.

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    Re: Understanding SWG Output levels

    Did you try taking some water from the outflow nozzles directly (with a tube) when the SWG is running and testing the FC then compare it to the pool? That will tell you if the dern thing is even generating. I think that would be a first step.

    From my first look the specs of the generator should be able to maintain this pool. I don't know what the effects of new plaster have on the chem for SWG, I recall there is, but perhaps someone else can chime in on that.
    20K IG gunite with attached spa, dark plaster and lava rock waterfall, very 90's. Pool equip refit in 2005 with all Sta-Rite cartridge filter, pump, and heater; Polaris sweep; Goldline Controller(Hayward) with T-Cell-15 SWG

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    Mod Squad pooldv's Avatar
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    Re: Understanding SWG Output levels

    New plaster has no impact. The most common cause for an SWG "not keeping up" is algae getting a start in the pool due to low chlorine levels. It is easy to verify this by performing the Overnight Chlorine Loss Test to see if there is something growing in the water consuming the chlorine.
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    Re: Understanding SWG Output levels

    I know the OCLT and that's on the list of things to tackle.

    What's the math to determine the the 'hourly' output of the cell, if everything else is perfect. Is the .72 lbs. per day when it's running at 100% for 24 hrs?. So could I do:

    .72 / 24 = .03 lbs per hour @100%? So then:
    .03 lbs per hour x 8 hours = .24 lbs of chlorine gas.

    According to pool math that would raise FC in 10,000 gallons by 2.9. If I run those 8 hours at night, I should see the FC up by about 2.9 in the morning theoretically?? Does that sound right??

    I get there are many other factors but I'm just looking for ways to get info and clues as to IF the SWG is producing anywhere close to what it should. If not it's brand new and needs to be warrantied. As I'm sure many of you know the service guys are going to do the minimum possible so if they can look through the clear housing of the cell and see the gas coming off they are going to say: "Nah, it works!" I want to have some evidence to push back, if needed. The OCLT will tell me if there are problems with the water, but not if there are problems with the cell.
    Appx. 39,000 gal., in-ground plaster. 48 SqFt Pentair DE grid filter, 1 HP Pentair single speed pump, Circupool RJ-60+ SWG (seen here). Currently using Cellulose instead of DE. Hayward XL suction sweep. TF-100.

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    Re: Understanding SWG Output levels

    The problem with your troubleshooting method is that if there is algae in the water you have no idea how much chlorine it is consuming.

    Pools with SWG's will often look clear but they are full of algae that is not visible because the SWG's make just enough chlorine to keep the algae from blooming, but they can't make enough chlorine to kill all the algae.

    If there isn't any other source of chlorine being added to the water then the SWG is working and the best step to take is the OCLT.

    If the OCLT passes then we need the test results posted and how you got them. Saying the test results are all good doesn't help us much.
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    Mod Squad pooldv's Avatar
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    Re: Understanding SWG Output levels

    So, why not eliminate the most likely issue first? There is no theoretical calculation that can be done. Even if we know the cell can produce 5 ppm per day you cannot calculate how much will be lost to the sun, organics, etc. The normal range of a pool is 2-4 ppm burn per day. But that is just a normal range, any pool can be different on any given day.

    Better than 90% of threads that start with "my SWG cannot keep up" end in a SLAM and the SWG performs fine for years after that.

    I guess if you really want to know how much FC your SWG is making you could turn it off and dose manually with bleach for 3 or 4 days to see how much FC your pool is actually consuming.
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