Another guy with algae

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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Joined: Mon 09 Jul, 2007 11:06

Another guy with algae

Postby skaggs3333 » Mon 09 Jul, 2007 11:19

24 foot round pool
Sand filter system

Saturation index: -0.93
Total Dissolved Solids 0
Free Chlorine 3.6
Total Chlorine 3.6
Combined Chlorine 0.0
pH 7.3
Cyanuric Acid 77
Copper 0
iron 0
Total Alkalinity 27
Adj. Total Alkalinity 5
Calcium hardness 79
Temperature 75

Alkalinity numbers were manually entered by cleric to allow the program to complete its


Went on Vacation for 10 days. Left niece and her BF in charge of pool. The pool was left

with out pump running. They discovered after a period of time that the pool was green. They

paniced and added many bags of shock. I returned home to a very green pool. At least they

killed the algea. Not being a very experianced pool owner I have been working with "the pool

store" The clorine levels were too high for the stores computer analizer to read until

today. The results are shown above. I have been adding earth to my sand filter and back

flushing as the presure gets high and flow to the pool is significantly diminished. Been

working on this for 5 days. Pool is murky green. The pool store girl says, "Oh my god!!

thats nothing" Ha! Anyway I am looking for help returning my pool to healthy state with

clear water. Will Flock do the trick? Girl says not yet. Filter for several more days before

that. What say you.

chem geek
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Postby chem geek » Mon 09 Jul, 2007 12:10

If the CYA level is truly 77 (and you should really get your own Taylor K-2006 test kit and not trust pool store numbers), then it will take 40% of this level, or 31 ppm FC to shock the pool to kill all the algae. Technically, you could use a lower FC level, but it will take longer, but I wouldn't go below 20 ppm FC in trying to clear the pool of algae. You will need to add chlorine frequently to maintain the high shock level of chlorine -- the algae will consume it quickly especially initially.

As you kill the algae it may settle to the bottom and you can vacuum to waste in that case. Even after you kill all the algae and clear your pool, with your high CYA level you will have to target an FC level of 11.5% of the CYA level or about 9 ppm FC and make sure the FC level never drops below 7.5% of the CYA level or 5.8 ppm FC in order to prevent green algae in the future. So you can see that a lower CYA level will let you have a lower FC level to maintain. Another option for you if you don't want to do a partial drain/refill to lower the CYA level is to use a weekly maintenance dose of PolyQuat 60 algaecide to keep away algae.

Right now with your low FC level the algae is growing faster than you are killing it which is why this is taking so long. Get the FC level up high and keep it there until the following three things occur: 1) the pool is clear, 2) you measure very little (< 0.5 ppm FC) loss of chlorine overnight and 3) you measure very little (< 0.5 ppm) combined chlorine (CC).

You should only have to use a floc (OMNI Liquid Floc Plus) if you don't have a floor drain or have poor circulation in your pool. Shock levels of chlorine plus your filter should be able to clear the pool of algae on its own. To see how this is done on a pool during spring opening, look at this link .

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fighting algae

Postby kpnack » Sun 22 Jul, 2007 20:58

I believe in all the pool geek has to say because I am almost at my fights end with my algae. I have never seen my pool so clear. I do have algea grow every day or so but its getting better. My problem is the cya level so high it is 70 but Im still using liquid chlor every night and keeping the level high to fight the stuff. kpnack
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Postby Backglass » Mon 23 Jul, 2007 07:42

Follow chemgeeks advice and save the Floc until the very end. I would also wait on adding DE to your filter until the pool is relatively clear as right now you need to maximize your flow through your filter and turn over your water as much as possible.

Save the Floc & DE for the final "polish".
I'm no expert...just a long time pool owner. The real experts are at www . troublefreepool . com

Download Bleachcalc free at troublefreepool . com /files/BleachCalc262.exe and start saving money on chemicals.

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