recurring algae problem

[parkerman]

My pool, located in San Diego, was resurfaced last year with a medium grey plaster. After start up the pool company set the CYA to 60 PPM. Not knowing better, I used tablets for a few months and my CYA rose 80 PPM. On 2 separate occasions this summer algae growth has forced me to shock the pool following the "pool school" instructions using bleach and muriatic acid. However, both times the algae returned within a few weeks. Being at the upper end of the CYA spectrum, I suspected that this might be impeding my efforts. 10 days ago I completed the shock process and passed the overnight test. The next day I treated with polyquat 60 for 24 hrs. I then backwashed the filter and drained 25% of the water to get my CYA down to 60 PPM. Since then I've checked my levels daily and kept my FC between 5 and 9 PPM. PH has been between 7.4 and 7.8. All testing is done with the recommended Taylor 2006 kit. Now 10 days later I see algae forming on the vertical edges of the stairs in the shallow end. This is usually where it starts and then it spreads around the entire surface of the pool. It appears to be green, but the true color could be skewed by the grey plaster. Oddly it only grows on plaster, never the vacuum or the vacuum hose which remain in the pool 24/7. The water itself remains clear.

I'm at a loss as to how algae can be taking root in a pool with ideal levels of free chlorine and the following parameters.
DE filter runs 9 hrs / day
Alk = 190
FC = 5-9
CC = 0
CYA = 60
pH = 7.4 - 7.8

Anyone have any ideas as to what the problem might be? I am guilty of not brushing my pool. In fact in the past 10 days I did not run the vacuum or brush the sides. Could this be enough to seed the problem?

 

[duraleigh]

parkerman,

Welcome to the forum. Algae establishes in pools that have inadequate chlorine....period. Rather than dwell on how your algae got started, I would get rid of it. You get rid of it by SLAMming the pool per the article in Pool School. Brush, vacuum and run your pump 24/7 during the process.

While your test results look fine, just keep in mind that the algae is in your pool because your chlorine has been inadequate....no other reason.

Follow the SLAM process correctly and the algae will go away. It will only reoccur if you allow the chlorine to fall too low and/or fail to practice good maintenance technique like vacuuming, brushing, etc.

Mark92677,

Controlling phosphates are a completely unnecessary part of pool water management. Thousands of us here on the forum never test for them and never will. Google "phosphates" here on the forum and read more about the logic behind ignoring them.

 

[Butterfly]

Welcome to the forum, parkerman

+1, what duraleigh said, ignore phosphates.

If you passed all three tests to be done with the SLAM process (see red lines in my sig), then you may have Mustard Algae.

It is a persistent type of algae that goes away at normal shock levels only to reappear when levels drop back to maintenance levels.

You can read about mustard algae here and see if you think your pool fits the definition:
pool-school/mustard_algae

Anyone have any ideas as to what the problem might be? I am guilty of not brushing my pool. In fact in the past 10 days I did not run the vacuum or brush the sides. Could this be enough to seed the problem?

Very possible. Also, how is the circulation in your pool? If you have any 'dead' areas where the circulation is poor, this could also contribute. Regardless of the cause, the SLAM process is the beginning of the cure.

 

[BoDarville]

Also check behind light fixtures and around ladders (if you have one). Here's an example of what was behind a light fixture of a pool that had clear water but was suffering from persistently high chlorine demand: http://www.troublefreepool.com/think-i-may-have-found-my-fc-demand-issue-t65957.html.

 

[parkerman]

Thanks for the feedback everyone. I've been reluctant to believe that I'm dealing with mustard algae, because it looks green and is not patchy. However, there is no denying it's fits the description of recurring post SLAM, once maintenance levels of chlorine are restored. Again the grey plaster might be skewing the true color of the algae. I had thought about treating the pool as if it were mustard algae, but my CYA was so high, it would've taken a ton of bleach and I thought the use of polyquat might remedy the situation as well. Now that I'm down to a CYA of 60 I may have to do the mustard algae super SLAM.

As for the light, I will remove that over the weekend. I see just one screw in the outer edge. Is that all it takes? Just back that out and pop the light out?

As for dead zones and circulation. I have 2 returns and they're almost right next to each other and pushing water the same direction. Which seems less than ideal. In addition I have a variable speed pump that I run at low energy saving RPM for 9 hrs. Should I consider to up the RPM for some of that time to get more vigorous circulation?

 

[Donldson]

Keep in mind that the mustard algae SLAM is the same during the SLAM portion, it is after the SLAM is completed that you raise the FC level to mustard algae levels for 24 hours.

Make sure the SLAM is seen clear through, the 3 criteria passed as well as zero visible algae and checking everywhere algae might be able to hide. After you pass everything if you want to raise your FC to mustard levels just to be sure then go for it. The more thorough you are in the SLAM the more likely this issue will finally clear up for you.

 

[Butterfly]

Moved phosphate discussion here: post572903.html#p572903

 

[Butterfly]

As for the light, I will remove that over the weekend. I see just one screw in the outer edge. Is that all it takes? Just back that out and pop the light out?
Yep, turn off power first. Did you remove the light? Did you find anything?

As for dead zones and circulation. I have 2 returns and they're almost right next to each other and pushing water the same direction. Which seems less than ideal. In addition I have a variable speed pump that I run at low energy saving RPM for 9 hrs. Should I consider to up the RPM for some of that time to get more vigorous circulation?
Yes, that sounds like a plan. But, nothing replaces brushing including all the nooks and crannies.

Got an update for us?

 

[danacc]

On the light--flip the breaker off first.