Green Cloudy Water After Heavy Rain

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mpride

mpride

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May 23, 2008
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Sugar Land Texas
I'm concerned about my pool water for the first time in the almost 3 years we have had the pool. It's a 9300 gallon concrete pool. It has a salt water generator. After about 6 inches of rain yesterday in a 2 hour period I noticed this morning that the pool water was a light green and slightly cloudy so I immediately tested the water and turn on the superchlorinate function. I didn't see and combined chlorine so I was curious if the green I'm seeing is algae or not. I also was unable to get a good CYA reading. My last reading was 70 and I haven't added any to the pool but my reading was over 100. I'm still running the chlorinator and haven't tested the pool water again but here are the readings from this morning:

PH - 8.0 (I've added acid to take care of this)
FC - 2
CC - 0
TC - 0
TA - 60
CH - 410 (I know it's high, my fill water is the problem)
CYA - 100+ ?????
Borates - 50
Salt - 2300 (I had to add salt)

So am I on the verge of my first encounter with algae or am I ok?
 
If your CYA is that high, then your FC level is way too low and yes, algae could then be growing. I suggest shocking your pool with chlorinating liquid or bleach. The superchlorinate function isn't going to be able to get the chlorine level up fast enough if there is too much algae already growing. Most likely, the rain blew in organic contaminants that depleted the chlorine level allowing algae to start growing. I'd add at least 25 ppm FC if not more right away (unsure of your true CYA level). The sooner you knock it out, the better.
 
Thanks for the quick reply. I think i knew the answer but was hoping I was wrong.

I need to ask one more question. I'm using the pool calculator to determine home much bleach will have to be added to move from a reading of 2 to a reading of 25. It looks like its telling me that 444oz of 6% bleach to bring it up to 25. Does that sound close? This assumes a CYA reading of 70 or so.
 
I got the 100 reading today after the rains. However, I know that my cya level was 70 just a few days ago and none has been added. I'm currently waiting on my wife to get home with the bleach. Does 444 oz of beach sound about right to get it to shock level?
 
Looks like all is well this morning. I'll still keep a close watch on it over the next few days though.

This was my first real scare with algae in the pool. I just want to say thanks to you guys for your help! It is very much appreciated!

:goodjob:
 
I'd question that CYA reading. Since it relies on turbidity - cloudiness- and the water is already cloudy, a false high reading seems not only possible, but probable. CYA doesn't just appear out of nowhere.

That's why regular testing and a log are useful. If a reading suddenly changes dramatically, you know there's something wrong....usually with the test! Just this morning my CH wouldn't turn colors, and it was already 200ppm over the last reading. And then the lightbulb went off, and I realized I was using a 25 ml sample instead of the usual 10ml.
 
I tested CYA this morning and it registered just north of 70. I had a measured 70 just a few days before the rains and a 70 is what I would have expected so that is back to normal also.

I didn't really enjoy this little episode but I will say that I learned a few things that will help me in the future.
 

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