High FC but algae won't clear up

Algae problems in swimming pool water.
Green (cloudy) water or slimy pool walls.
Black algae. Mustard algae. Pink or white pool mold.
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High FC but algae won't clear up

Postby kmd » Tue 13 May, 2008 06:07

Hi everyone - great board you have here. I'm hoping to get some help, I'm kind of at a loss here...

Using HTH test strips every few hours:

TH 200
FC 10+++ (the pad on the strip is so dark it's almost black)
PH 8.4 (it was stabilized at 7.2 before I shocked though)
TA 120
CYA 30-50

I have a 4-year-old 11,000 gallon above-ground pool and sand filter. I forget the brand of the filter but the handle has a W on it. The weather here has been overcast and cool, if that makes a difference.

Uncovered the pool on Sunday and the water was dark brown, worse than any other year so far. I got up on the ladder and started pulling out leaves. I think I got the bulk of them out but I can't see more than an inch into the water. Tested and adjusted PH, then started shocking.

Sunday afternoon I put 8 bags of calcium hypochloride 54% in, and by Sunday evening the water had improved to a murky dark green. Filter is running 24/7, pressure has remained constant at 4.

Sunday night I tested the water before bed and the FC was still off the charts so I went to bed and dreamt all night of a pool filled with dead algae by morning.

Monday morning went out to the pool at 6am and the water was still a murky dark green. FC was still off the charts but the shade of purple was ever so slightly lighter the night before. I added another 6 bags of shock and a gallon of algaecide. Spent most of the day on the ladder brushing the liner, pulling out some leaves and basically willing the algae to DIE.

By Monday evening the water had improved to a pea-soup green and I could see in about 2 inches deep. FC still off the charts at a very dark purple, almost black. Thinking more shock might speed up the process, I added another 6 bags and brushed the liner some more.

This morning I ran outside at 6am, thinking that HAD to work but the water has shown no improvement since yesterday... it's the exact same murky pea-soup green. The FC held overnight at a very dark purple on the test strip.

So since Sunday afternoon I've used 20 pounds of shock on an 11,000 gallon pool. Overkill? I know it's only been 36 hours but I don't remember it ever taking so long to show a marked improvement when I shocked. I live in the boonies and pool supply stores are a daytrip away so I'm relying on my test strips, my very basic knowledge of pool chemistry and the internet.

Any thoughts or advice? Thanks so much.

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Postby muss08 » Tue 13 May, 2008 06:29

First you need to get your pH down to 7.4-7.6. Chlorine is not very effective when the pH is that high. Second, get a better test kit than strips. Strips aren't very accurate. I use the Taylor K 2006. Keep brushing and backwashing the filter. Dont bother with the algaecide if you're shocking.
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Postby Pooltech32 » Wed 14 May, 2008 00:28

4 psi seems very low? keep backwashing and let the filter do it's job.
Pool repair guy

Postby Guest » Sun 18 May, 2008 16:37

The advice on a better method of testing is the first thing you should follow.. also when you closed the pool, did you use a copper algaecide to winterize or in conjunction with your current treatment?? Does your pool have a heater or copper pipes of any kind?? What kind of fill water do you have?? Well?? City?? I would suggest a Lamotte Color-Q, easy to use and very accurate, what i use on a daily basis. Also, a water test a the store would be a good idea at this point, and have them test for metals, as shocking heavily with metals present in conjunction with the high pH of the cal hypo and your pool water would cause a green or colored tint to sometimes get worse with shocking. Also, high combined chlorine will cause a green tint. How old is the media in your filter, and did you chemically clean your filter at the end of last season?? The W on your filter probably stands for Waterway, by the way. For future reference, try a good flocculant FIRST next time, generally the quickest way to clear the pool, and make sure to vac to waste, and always remove all solids and organics from the bottom with a leaf net before beginning any chemical treatment whatsoever
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