Chlorine 'disappearing'

[ST47]

Hi! I own a 12,500 gallon vinyl lined above ground pool. We use a sand filter and a chlorine floater with tablets. We have low chlorine, and have had low chlorine all season, even after shocking with 1-2 lbs of trichlor at a time. We would wait 5 minutes and a drop test(DPD, but OT and strips had same results)showed 5-10 ppm of chlorine. The next morning, the chlorine would be gone, 0 ppm free and <2 ppm combined. The two things I thought of were low CYA(which turned out to be about 80 ppm) and low pH(about 7.0), neither of which is low enough. We added Soda Ash(2 lbs) for TA last week, and apart from the Leslie's Opening Kit and a blue clarifing cube of slimy goo(which I just removed), we have added no other chemicals. When we opened it(2-3 mos. ago) the water was green, but that was better w/shock and aforementioned opening chemicals. There has been some brown-colored silt along seams, but that has been there for as long as I can remember, and any water current around it will push it up. The liner is beginning to be bleached, however it is 5+ yrs. old. Also the liner is slippery along the sides. Less than 5 hrs. ago we added 2 lbs. of trichlor. 15 mins. later the chlorine was well off the scale on the DPD drop test, now it is 2-3 ppm with no combined. Hardness is around 200 ppm, and metals(copper/iron) were not present. I'm not sure what this could be, and hope someone can help!

Thanks

[ST47]

Read some other posts, is there a test for Ammonia due to leaf decay or other organics that Leslies would have?

[ST47]

anyone here!

[pk4217]

your TA?

[Daveski]

Sounds like you are trying to stay on top of things.

I'm still fairly new. I used a reputable smaller pool shop and had good luck in the maintenence. We tried Leslies' pool supplies out this year and had aweful luck with getting the pool looking normal. (water tests)

I went back to my small pool shop that took longer to drive to - and they had me adding all sorts chemicals to get it balanced (the Leslie's pool shop just said, "add shock").

Big difference within 24 hrs with my regular place vs. Leslies. My advise - find another pool shop/dealer

Dave

[Daveski]

Sounds like you are trying to stay on top of things.

I'm still fairly new. I used a reputable smaller pool shop and had good luck in the maintenence. We tried Leslies' pool supplies out this year and had aweful luck with getting the pool looking normal. (water tests)

I went back to my small pool shop that took longer to drive to - and they had me adding all sorts chemicals to get it balanced (the Leslie's pool shop just said, "add shock").

Big difference within 24 hrs with my regular place vs. Leslies. My advise - find another pool shop/dealer

Dave

[me]

Hi! I own a 12,500 gallon vinyl lined above ground pool. We use a sand filter and a chlorine floater with tablets. We have low chlorine, and have had low chlorine all season, even after shocking with 1-2 lbs of trichlor at a time. We would wait 5 minutes and a drop test(DPD, but OT and strips had same results)showed 5-10 ppm of chlorine. The next morning, the chlorine would be gone, 0 ppm free and <2 ppm combined. The two things I thought of were low CYA(which turned out to be about 80 ppm) and low pH(about 7.0), neither of which is low enough. We added Soda Ash(2 lbs) for TA last week, and apart from the Leslie's Opening Kit and a blue clarifing cube of slimy goo(which I just removed), we have added no other chemicals. When we opened it(2-3 mos. ago) the water was green, but that was better w/shock and aforementioned opening chemicals. There has been some brown-colored silt along seams, but that has been there for as long as I can remember, and any water current around it will push it up. The liner is beginning to be bleached, however it is 5+ yrs. old. Also the liner is slippery along the sides. Less than 5 hrs. ago we added 2 lbs. of trichlor. 15 mins. later the chlorine was well off the scale on the DPD drop test, now it is 2-3 ppm with no combined. Hardness is around 200 ppm, and metals(copper/iron) were not present. I'm not sure what this could be, and hope someone can help!

Thanks

Don't shock with trichlor, use an unstabilized chlorine instead (bleach, calcium hypochlorite). You need 2.6 ounces of 65% calcium hypochlorite for 1 ppm for your water volume. Trichlor by weight is 54% stabilizer and 45% chlorine.

DPD only goes to about 5 ppm chlorine, DPD-FAS goes to 50. For a quick go-nogo use OTO.

The pH at that level is ideal for shocking, you may want to increase it after the shock.

With a CYA of 80, it sounds like there's a chlorine demand somewhere, otherwise the chlorine residual should last. I'm intrigued by the walls being slippery and by the brown colored 'things' at the seams of the liner. It may indicate algae or iron deposits but you say iron is not present. And as you say water current will push it up.

To make a long story short your're fighting something. Chlorine will oxidize out any organics, I would try superchlorinating to 20 ppm of calcium hypo, that's about 6 pounds of 65% strength. Remember to dissolve it first in a bucket of hot water as to not bleach your liner. If all is well you should wind up with a residual, especially with 80 ppm CYA. Water will become a bit cloudy as the calcium takes a bit longer to dissolve, so expect cloudy water for maybe a day/two days at that volume.

[mjcox]

Just curious if the problem was resolved and, if so, what resolved it. I am having troubles keeping chlorine in my pool also and I am not sure of what is causing it.