My pool's love affair with algae

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Sep 11, 2010
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Orange County, CA
I'm wondering why I keep having problems with algae. I don't seem to be able to avoid the stuff. I think it was last year someone told me that algae doesn't necessarily read and follow the rules we discuss here :) Thanks to TFP, I know what to do to get rid of it when I get it. That's not the problem. Here's a little recap:

Last year I tried Fiber Clear in the filter. I thought that was the solution. I had to backwash the filter pretty much every 2 weeks, which I hated, but I thought I finally had a solution to my algae problem...until I got algae a couple of times. So, it wasn't the solution :( This year I'm back on DE. All the grids were also replaced this year.

Sometimes in the past I got algae because I let my FC get too low. That's not my problem now. I'm usually running FC around 7 or 8. And I still get algae!

Here's tonight's chemical test.

  • FC 11.0 (It's high because I had algae and added chlorine. But, when I got algae, it was around 7.5 - 8.0)
  • CC 0.5 (I know that means 0)
  • pH 7.3 (it's low because adding chlorine raises the pH and the chemical feeder adds acid. Normally it's around 7.4)
  • TA 60
  • CH 625 (It's high. People here have told me I can go with it if I keep the water balanced. I'm in California where we have a drought and empything part of the pool to refill isn't an option at the moment.)
  • Salt 3000
  • CYA 60

This year I'm experimenting with a chemical pool cover (Heatsavr). That's something new in the water. I don't know if that affects anything? Still, I've had algae problems in years past before I started using it.

Are pebble surfaces more susceptible to algae? (maybe it's easier to get started in one of the

Any thoughts?
 
I'm not sure, Could it be hiding behind your pool light or behind your stairs. What does the water look like? With a cya of 60 as long as you are maintaining the target FC of 7 to 8 you should be fine.
 
Pebble is not more prone to Algae, and whomever told you Algae doesn't play by our rules is simply mistaken. I'm not saying that out of anger, it's just not true, and they haven't played by our rules to find out the truth.

Algae gets into a pool for one reason, and that is low FC. At some point you have had too low FC more than you realize. Its very likely as well that when you have had green in the past, you never fully killed it all with a good SLAM and always had some lurking and ready to spring back. I suggest a full and complete SLAM and watch the FC very closely from here out. If you do, there will be no more problems with Algae.
 
Another thing to look at....

When I first took over the maintenance of the pool at my condo complex, I always had to keep my chlorine level at least 1ppm above what the Chlorine/CYA chart said to use. If my FC got down to the minimum for my CYA, the water would get cloudy. I cleaned out behind the light, which seemed to help a little, and I adjusted the return jets to make sure I was getting decent circulation throughout the pool.

Then reading a thread here on TFP, I realized that my skimmer was missing its float valve (aka diverter valve). Like many in-ground pools, my floor drains are hooked up to one of the skimmers, not directly back to the pump. The float valve allows you to adjust how the suction is distributed between the skimmer and the drains. If the float valve is missing, then the floor drains get ZERO suction. (See this post for what to look for. Note that both holes in the skimmer have pipes attached, and go on for more than 6 inches.)

So beneath the drain covers, there was plenty of light and plenty of gunk to feed the algae, and the algae was protected from the chlorinated water above. So algae was continually coming up out of the drains and getting killed by the chlorine, which was why my pool water wasn't perfectly clear. And whenever the chlorine level dropped low enough, the chlorine couldn't keep up with the algae coming out of the drains.

Installing a float valve fixed the problem. Within an hour, my filter pressure shot way up to the point where I had zero water flow. That tells you how much crud was hiding down behind the drain covers. IIRC, I had to backwash twice that day.
 
Thanks for the thoughts. I didn't realize that after killing off the algae that something could remain behind and come back to life even with higher FC levels. I've never tried cleaning behind the light. I better give that a look (and maybe that's my motivation to replace my light at the same time, since one of the colors of the LEDs died last year).

The water looks clear. In fact, even when I have algae, the water is fairly clear until I brush it off. I usually catch it fairly quickly and the water never gets that cloudy.

I thought if I did a SLAM and didn't take it all the way to the shock level that it just took longer to kill off the algae. I didn't take it to the shock level this time; I just raised the level, brushed the sides, and it all seemed to go away. It looks good now, but I guess I better check behind the light and SLAM it before it comes back to visit again.
 
Oh, I forgot to mention: yes, the diverter valve is in place, so it's pulling from both the skimmer and the drain. Funny...I was at a friend's house a few years ago for a party and helped figure out how to get the spa going, as it wasn't working. I also found the diverter wasn't in the skimmer. She told me her pool man removed it. I told her that needs to be there so the water circulates properly and put it back in. I have no idea why he removed it.
 

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I finally got around to checking things, like behind the light. There was a bunch of dirt/sediment/whatever in the niche. I don't know if any algae was mixed in. It's gone now. I also cleaned out a few other places where it might lurk and then SLAMed the pool. Hopefully that takes care of things now. Thanks for the suggestions.
 
If you SLAMmed the pool, that means you followed the article in Pool School precisely and met the following criteria....
1. Your pool water is sparkling and no signs of algae
2. Your CC's are .5ppm or less
3. You can hold your FC overnight without losing more than 1ppm.

If you didn't meet all three of those criteria, you didn't SLAM.

This thread indicates you have played patty-cake with your algae issues in the past. You must hit algae with a sledge-hammer (full SLAM value) and then maintain adequate chlorine once you have completed the SLAM.
 
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