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Thread: Need clarification on CYA --> FC ratios etc

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    Need clarification on CYA --> FC ratios etc

    Ok, I've learned a lot at this website, but for the life of me I just don't understand the purpose of keeping CYA so low, and not using trichlor. What is the biggest problem with having a cya so high? Every single person I've talked to, even including the guys that run Wet Republic Day Club here in Vegas. They use liquid chlorine, but the guy says he just uses pucks at his own house. I asked him about cya, and everyone says that you have to replace the water eventually anyways every couple years. Can someone explain this to me in simple mans terms? What is the harm? I just don't understand for some reason.

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    I have no problem pouring chlorine in every day, and monitoring it myself, but the simple chlorine test for me it's hard to tell what my actual chlorine level is (based on how yellow it is). Right now I'm using leftover trichlor pucks to get my cya up above 20 since my refill. I've checked it every 4-5 days and it's still low, so I'm not too worried right now. Pool season is coming quickly, and I'm aiming to be an expert by April.
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    Mod Squad JohnT's Avatar
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    Re: Need clarification on CYA --> FC ratios etc

    If you get the FAS-DPD chlorine test, there is no judgement issue to the result. When the water turns clear, you know what the chlorine level is.

    When your CYA is high, your chlorine is less effective. With low CYA, 10ppm FC may be insanely high, but with high CYA it may be almost completely ineffective at killing pathogens and algae. If you slip up with high CYA and get an algae bloom, it can be very difficult to control it because the CYA reduces the effectiveness of the chlorine.

    Look at the Chlorine CYA Chart Those target FC levels and shock levels are the same effective chlorine levels. When your CYA is at 100ppm, it takes 12ppm FC to make your water safe and 39ppm to shock the pool.
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    Mod Squad jblizzle's Avatar
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    Re: Need clarification on CYA --> FC ratios etc

    There are only 2 reasons to have to ever replace the water: 1. The CYA gets too high or 2. The CH gets too high

    As CYA goes up, the FC level required to prevent algae goes up. See the FC/CYA Chart. Pucks will only add a certain amount of FC at the rate they dissolve, but the whole time the CYA is rising. Eventually, the FC added will not be high enough to prevent algae and you will get a bloom. Then, if you go to the pool store, you will buy a whole bunch of stuff to try to kill the algae (some of which may raise the CYA even higher), until they can not figure out why the pool will not clear and will suggest you drain and refill. OR, you will follow the SLAM Process to clear up the pool and you can see in the chart that as the CYA get higher, the FC level required to SLAM goes WAY up too. Either, way you are wasting a lot of money trying to clear up the algae, where if you just kept the CYA level in range and kept adequate FC in the water, you would never have gotten algae in the first place.

    CH will always rise due to topping off the pool as water evaporates out. How fast depends on what the CH level is in your tap water, how much evaporation you get, and how much rain you get. CH may never be a problem for many people, but for others like us in the desert with high CH fill water, the CH may get pretty high in 3-4 years which requires some water change to keep the CH reasonable. If the CH gets too high and the pH is too high, you can get ugly calcium scaling all through the pool which is difficult and expensive to get rid of.

    Tablet can work for some people who have short swim seasons, lots of rain, and do a partial drain for the winter. The CYA will climb over the summer, but the rain and drain in the winter can lower it before next season.

    The key is testing and understanding of your pool.
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    Re: Need clarification on CYA --> FC ratios etc

    Quote Originally Posted by jblizzle View Post
    There are only 2 reasons to have to ever replace the water: 1. The CYA gets too high or 2. The CH gets too high

    As CYA goes up, the FC level required to prevent algae goes up. See the FC/CYA Chart. Pucks will only add a certain amount of FC at the rate they dissolve, but the whole time the CYA is rising. Eventually, the FC added will not be high enough to prevent algae and you will get a bloom. Then, if you go to the pool store, you will buy a whole bunch of stuff to try to kill the algae (some of which may raise the CYA even higher), until they can not figure out why the pool will not clear and will suggest you drain and refill. OR, you will follow the SLAM Process to clear up the pool and you can see in the chart that as the CYA get higher, the FC level required to SLAM goes WAY up too. Either, way you are wasting a lot of money trying to clear up the algae, where if you just kept the CYA level in range and kept adequate FC in the water, you would never have gotten algae in the first place.

    CH will always rise due to topping off the pool as water evaporates out. How fast depends on what the CH level is in your tap water, how much evaporation you get, and how much rain you get. CH may never be a problem for many people, but for others like us in the desert with high CH fill water, the CH may get pretty high in 3-4 years which requires some water change to keep the CH reasonable. If the CH gets too high and the pH is too high, you can get ugly calcium scaling all through the pool which is difficult and expensive to get rid of.

    Tablet can work for some people who have short swim seasons, lots of rain, and do a partial drain for the winter. The CYA will climb over the summer, but the rain and drain in the winter can lower it before next season.

    The key is testing and understanding of your pool.
    Well said! I just copied your summary and plan to use it when friends ask why I don't use pucks!
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    Re: Need clarification on CYA --> FC ratios etc

    We don't recommend keeping it so low. About 40-50 for non salt pools. If that is what you mean though...here is why.

    Keeping it here is prime. You get Chlorine buffering and sunlight protection for the Chlorine at optimum rates for usage and dosage. It prevents premature drain and refill. With good makeup water quality, a regular drain and refill is never needed. Saying it is as a blanket statement simply isn't true. Putting things in a pool like Cal-Hypo, TriChlor and Dichlor accelerate the need to dilute as they add Calcium and Cya respectively.

    If a pool has high Cya, it takes more Chlorine to do the job, and makes it very hard to clear an Algae bloom if you get one. Reason being is that high Cya, demands even higher FC to kill the Algae. High Cya is the number one proble we see here. People come every summer with an Algae bloom they cant beat and time after time it is Cya related. You need a little more Cya in a SWG pool, but this is why we suggest what we do.

    The guys you are talking too use Bleach for its low cost mainly.

    Hope this helps...
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    Re: Need clarification on CYA --> FC ratios etc

    Quote Originally Posted by pragmatic View Post
    Well said! I just copied your summary and plan to use it when friends ask why I don't use pucks!
    Agreed, this is what I was looking for. Maybe post an answer like this as I've been hard pressed to understand the relationship.
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    Mod Squad jblizzle's Avatar
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    Re: Need clarification on CYA --> FC ratios etc

    Thanks for the Kudos

    Let me add another thing about trichlor pucks. They are very acidic. If you put them in your skimmer (we NEVER recommend this), they can damage the basket and the equipment, especially if you do not run the pump 24/7. In the stagnant water in the skimmer the pH can get VERY low when the pump is not on and then that is sucked into your pump and filter. Since they are so acidic, they can drive the entire pool's pH and TA too low if you are not careful which can cause damage to the equipment and pool itself.

    Most of this is covered in Pool School here: How to Chlorinate Your Pool
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    Re: Need clarification on CYA --> FC ratios etc

    The ChlorineCYA chart is nice, but it doesn't give you any info other than the ratio you should work on. It says nothing about a suggested # you should maintain. How do I get to a point when lets say, my cya is at 30, and I want to have a certain amount of chlorine added every day to maintain an fc of 4? Do I have to do the advanced chlorine test once a week etc? As I said before, to me there's yellow and then dark yellow on my basic tester. Should I expect to add chlorine every day or every other day once I get these levels figured out?
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    Mod Squad jblizzle's Avatar
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    Re: Need clarification on CYA --> FC ratios etc

    The chart does not have ratios it tells you th FC level that must be maintained. You need to use the FAS-DPD daily and add chlorine daily to learn your pool. Then you can likely get by with testing less often, but still adding chlorine daily.
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    Re: Need clarification on CYA --> FC ratios etc

    Chlorine consumption will vary from day to day, depending on level of use the pool gets, along with other mostly weather related factors, like amount of sunlight, temperature, amount of wind blown organic material that enters the water, rain, etc. The longer you go between testing the higher the chance that your going to accidentally drop below your FC minimums due to mis-estimation of your Chlorine burn rate the longer between dosing the more swing your going to have on your Chlorine level. Many of us that do manual addition of chlorine (or have done it in the past) feel that a daily routine dosage works best as one is less like to accidentally loose track and skip an additional day. As to testing personally I think it is best to test often until you get to know your pool, and then testing can be reduced to perhaps twice per week, maybe once per week if you have a particularly stable pool. The time this takes once you get into the routine will be much less than the typical person spends brushing their teeth each day. Note I am not suggesting running a full bank of tests each times, probably just FC and pH, maybe just FC if your pH tends to be stable, and pH once every week or two. The optional Speed Stir greatly speeds up the FAS-DPD testing, so much so that personally I almost never use the OTO (shades of yellow) "quick test" on the pool.

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    Re: Need clarification on CYA --> FC ratios etc

    +1 for Ike and Blizzle. All good points. Over time, you will get a "feel" for how much Chlorine is consumed, but at first, you should be testing with the FAS DPD test daily.
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    Re: Need clarification on CYA --> FC ratios etc

    Fair enough. That being said, right now my trichlor tabs "should" keep my chlorine level in range while I'm slowly raising my cya? Especially that it's still relatively cool out? Regardless I think I'm going to start doing the chlorine test to get a feel .
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    Re: Need clarification on CYA --> FC ratios etc

    Quote Originally Posted by Enzman View Post
    That being said, right now my trichlor tabs "should" keep my chlorine level in range while I'm slowly raising my cya?
    Yes, but you still need to do the test to verify. Plus, the only way to develop the feel and get to the point where you can put your pool on autopilot is to get plenty of data to watch the trend.
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