Why is my pool so dirty!!!

[chem geek]

The reason that most SWG manufacturers want a high CYA level is that the salt cell operates more efficiently if there is higher CYA because the CYA combines with the generated hypochlorous acid (chlorine; HOCl) fast enough to keep the concentration of chlorine and dissolved chlorine gas low enough to make the generation of the chlorine gas at the plate efficient. If there were too little CYA or no CYA, then there would be a buildup of chlorine gas and hypochlorous acid near the generating plate and this would slow down the chlorine production rate (since the electrochemistry is a chemical reaction and like all reactions, they slow down when there are more "products").

Though I would personally prefer that the SWG manufacturers redesign their equipment to operate more efficiently at lower CYA levels (say, 30-40 ppm), this would probably require larger plate areas and longer cells. At any rate, you don't have much choice with your system so to operate efficiently, you should keep the CYA at the recommended level. So that just leaves the Free Chlorine (FC) level as the variable you can readily control and it is easy to simply set the chlorinator to run longer or at higher power (I would prefer running longer at lower power, if you have a choice) to get the FC to at least 3 or more depending on what is needed to keep algae at bay in your pool. The best way to increase your chlorinator lifespan is to run with the recommended level of CYA so that it operates at the highest efficiency. The higher FC level isn't going to burn out your chlorinator that much faster and besides, you don't have any choice since you must have that FC level to prevent algae. Yes, you could experiment and lower your CYA level and have a lower FC level to match (say, 30 ppm CYA with 1.5 ppm FC or more) and see if you can generate this at an overall lower time/power level on your chlorinator, but I bet that you will find that the chlorinator has to run a really long time to generate even a small amount of chlorine when the CYA is low (30-40 ppm).

The SWG users on this forum have found that the efficiency of the SWG is not linear with respect to CYA. In other words, at 60 ppm you aren't twice as efficient as 30 ppm and there may be a large jump from 60 to 70 to 80 ppm in efficiency. Unfortunately with CYA, it isn't easy to experiment with. You can increase it without too much trouble, but decreasing CYA requires drain and refill of part of your pool water. More technical info about the requirement for CYA in an SWG pool may be found at this thread. It might be best for you to get to 80 ppm CYA and see if there is a large efficiency jump and then stay there and adjust FC higher instead (and read on for more ways to reduce chlorine consumption and therefore reduce your chlorinator's output and "on" time).

If you want to minimize the output of your SWG, then one thing you can do is to add a weekly maintenance dose of algaecide which will help stop the algae and will reduce chlorine consumption. In fact, with your algae, your SWG is working harder to even maintain 1 ppm FC so you may be partly fooled into thinking that it will need to work that hard after your algae is gone and with higher FC -- it may actually not need to be on as long (it's hard to know for sure). The best algaecide to use would be PolyQuat 60%, but weekly maintenance will get expensive. Another alternative that some users of this forum have found to be very useful (and is only a one-time cost) is to add 50 ppm Borates (measured as ppm Boron) which can be obtained from Borax (sodium tetraborate decahydrate). This is not only an algaecide and will cut down your chlorine consumption, but is also a pH buffer and will let you lower your TA to around 90 which will also help reduce the rise in pH (so you'll need to add less acid on a regular basis). Be aware that Borax is a base/alkaline so you'll be adding acid along with it, at least when initially adding it to the pool. You can find more about using Borax at this thread.

Richard

[bizbad]

That is interesting about the Borax. PH creep has always been a pain to me. I add a quart of acid a week to keep my ph down. The algecide benefit would be a tremendous bonus.

[bizbad]

Just wanted to report in. I chose to raise the clorine level to 35 ppm for 60 hours with pump running. I brushed each day. It has been two days since I stopped brushing and it still looks good. If I dont need to brush tomorrow I will know that I have won the battle. I am going to add Borax to the pool next week to see if I can level off the acid usage and provide some algecide benefits as well. I hope it works! Thanks for help.

[chem geek]

Just wanted to report in. I chose to raise the clorine level to 35 ppm for 60 hours with pump running. I brushed each day. It has been two days since I stopped brushing and it still looks good. If I dont need to brush tomorrow I will know that I have won the battle. I am going to add Borax to the pool next week to see if I can level off the acid usage and provide some algecide benefits as well. I hope it works! Thanks for help.

Great news about your pool getting cleared! You'll know that you've gotten all the algae if your FC level holds up overnight (or not in sunlight) and you have no (or < 0.5 ppm) CC. The 35 ppm probably worked because you started out at a little lower pH and, most importantly, the temperatures are cooler now so the algae isn't growing as fast. At any rate, it's good to know.

Don't forget to lower your TA to 90 or even 80 as that will also help. Follow the procedure at this post to lower your TA.

Your biggest problem now will be how to get your FC level back down if there isn't any sun to break it down, but technically with a CYA of 70 ppm and an FC of 35 ppm, the disinfecting (and oxidizing) chlorine level is at the same level as it would be if you had 1.0 ppm FC with no CYA. Though I would be confident enough to actually swim in such water, I'm a nutty chem geek. There's always the possibility that the chlorine bound to CYA does something nasty we don't know about (though it doesn't show up in ORP sensors, doesn't seem to kill any bugs, doesn't seem to oxidize anything, or do anything else that is detectable...). I did find that one can use hydrogen peroxide to lower chlorine levels rather than using sodium thiosulfate, so that was good news.

Richard