High CYA and Persistent Algae

Hello all,

First I must say thanks for providing such an informative forum. I have read through much of the site and believe I FINALLY have a decent understanding of my pool issues. For the last year or so, I have been battling a persistent algae issue. I haven't ever let it get completely out of control but have spent a ton of unnecessary money at the pools stores by buying into the phosphate removal pitch. I have also purchased the green to clean products which do a good job initially. Every time the algae reappears within a few days. Very frustrating!

I had my water tested and found that my CYA is 150! I dug through the wealth of information here and found that my chlorine wouldn't be effective unless it was between 8-15ppm. So, I stopped using my chlorine pucks and granular chlorine and purchased some bleach to super chlorinate. I ordered the Taylor k-2006 test kit which arrived today. Here are my results:

FC = 19.5
CC = 0
PH = 7.6
ALK = 100
CYA = 100+

My pool is 35k gallons.

I guess my two options are to keep my chlorine between 8-15 or drain my pool and refill. The strange thing is that I still have a little bit of algae in my pool on the walls and floor. Not sure why?! If I use bleach only, not the pucks/granular chlorine, through the winter is there a chance that I can get my CYA to a reasonable level? Any suggestions would be greatly appreciated.

Thanks,
Brian from Dallas, Texas

Since you have a K2006, and are already at CYA=100+ (150?), I'm not sure there's really a downside to running high chlorine -- using BLEACH! -- until your CYA comes down.

It won't hurt you or your pool, and it will allow you to dose 1x per week.

I would recommend taking it on up to 25 ppm, and then brushing. If at week's end, there's any trace at all of algae, take it up to 25 ppm again. Don't let it get below 15 ppm, till you are SURE the algae is gone.

Most people can swim at FC=25 ppm & CYA>100ppm with even noticing the chlorine, but you might want to wear your older swimsuits, and rinse them out in tap water when you finish.

Thanks, I appreciate the help!

Just wanted to welcome you to the forum!

Thanks! Just want to give an update and make sure I am following your advice correctly.

Sunday night I raised my chlorine level to 30ppm using bleach. I brushed and then vacuumed the pool and it looked great. I then tested the water again Monday fc=28, Tuesday fc=25. Today, I noticed that there are traces of algae on the pool walls. Ugh!

My water tests today:

FC=21
CC=0
PH=7.4
ALK=110
CH=600
CYA=100+

I am going to add more bleach and brush the sides again to hopefully knock it out for good. My filter pressure has not risen very much at all. Should I backwash anyways?

Looks good to me . . . sorta.

Your saturation index (pH + alk + ch) is out of sight. Once you're ready to close for winter, you may want to do something about that -- but it will mess up your pool for awhile when you do, so now's not the time. Just be careful to NOT add any alkalinity (baking soda) or calcium (calcium chloride). And do NOT let your pH go up: hold it below 7.4.

Your chlorine is high enough, so that to get accurate pH readings, you'll need to mix pool water 50:50 with distilled (not: bottled!) water before testing. Make sure it's "distilled" -- usually available in the bottled water section at Walmart -- and NOT anything else.

Also, keep your chlorine high and brush the pool out at least 1 cycle AFTER you think all the algae is gone. Then, and not before, you can let your chlorine drop.

First off, thanks for the continued advice. Just checking to see if I am following your instructions correctly.

I held the FC=25 and PH=7.4 for a week and there were little to no signs of any algae. The past couple of days I've let it drop to 21 and now there were signs of algae growing on the walls. Should I just brush and raise it back up past 25 again for a bit longer?

If you still have algae in the pool, then you need to raise it back up and hold it there, past the point where you think all the algae is gone. One good test for when to let it drop back down is when you can test at night after the sun is off the pool, and test again in the morning before the sun is on the pool, and see if you've lost chlorine overnight. If so, then you still have something in the water consuming it, so don't let it drift down yet.

Are you also putting any brushes, poles, pool toys, etc. in the pool while it's being shocked, to keep from re-introducing algae when you use them?

Might want to consider the use of Borates at 50 ppm, which acts as an algaecide and can be used in conjunction with regular shocking, HOWEVER, since Pooldoc has ponted out that you need to keep your pH low for now, I'll let him advise you on whether that might help in your situation.

Janet