Algae line on flagstone at water surface

[woody]

I have had this algae problem for some time now and can't seem to clear it. It is only located in 2 or 3 small locations and right at the water surface on my flagstone. I have used a steel wire brush on a drill and completely removed it, but it returned the next day. Apparently, it is embedded in the stone. I'm not sure what kind of algae this is. The water balance stays good, however lately cya is a little high. This line of algae stays there even when all values are near perfect.

FC 4.0
pH 7.6
TA 110
CYA 90

Here's a photo from a spot in the spa. You can see how clear the water is (water line just below the green algae line). Notice how there is no algae on the stones next to this one.

Anyone have any ideas on what this is and how to get rid of it?

 

[reebok]

looks like algae. my guess is easiest way to get rid of it is by raising your water level so the chlorinated water covers it and brushing. btw, your values are not fine. read pool school, particularly the chlorine/cya chart. pool-school/

 

[duraleigh]

Chlorine kills algae. You do not have enough chlorine for your current CYA level.

1. Raise the water level until the algae is immersed.

2. Raise your Chlorine level to 35ppm and Hold it There 24/7 until the algae is gone. The key words above are "hold it there"

 

[reebok]

duraleigh, with a spot or spots like that, is it really necessary to raise it to "clear your green swamp" levels of FC? of course his water could very well have a nascent bloom, but that's neither here nor there at this point.

 

[woody]

Thanks for the replies. This spot is in the spa that overflows into the pool. I cannot raise the level.

I agree that I need to raise my cl level (working on that now), but my cya has not always been this high. I recently raised it since the sun is burning too much chlorine. Meant to reach 75, not 90, but oh well.

Maybe a daily regement of concentrated chlorine (bleach) on these areas might do the trick?

 

[reebok]

yeah it should. rubbing a trichlor puck on there if you have one would really do well. borrow one if you have to. this is also a good read if you haven't seen it.
pool-school/water_balance_saltwater_generator
also, you don't need to be working on raising your fc by bumping up the swg. you need to add chlorine/bleach now and hope you don't have an algae bloom already in there waiting to happen. if you have a fas-dpd test I would highly recommend the overnight fc loss test which can be found in pool school.

 

[woody]

thanks reebok. I have kept the water very close to recommendations in the article for swg. The water has remained crystal clear since it was built 2 years ago with exception to hurricane ike. Took 1 week to clear that up. Never had any other algae problems.

Note that the water and all wall surfaces below are clear of any algae. It only appears above the water line. This make me think that the chlorine level may be high enough to keep it at bay in the water, but not out of the water.

Looks like I will need to use bleach anyway to get the fc up since the swg is on the blink. Waiting for the builder to make a warranty call. In the meantime, will need to use the puck chlorinator (and restock emergency pucks), but will boost with bleach.

I do have a Taylor fas-dpd kit and will conduct the fc loss test once I get the fc up to a respectable level.

 

[duraleigh]

In the meantime, will need to use the puck chlorinator (and restock emergency pucks),

You are only adding more CYA when you use the pucks.

Use chlorine and, yes, if you cannot get the water to that level, apply it directly.

Chlorine kills algae.

Pucks add CYA and you have too much already.

 

[Butterfly]

Hi woody,

I suggest you do the overnight test.

If you don't pass the test, you need to shock your pool.

 

[woody]

Thanks for the suggestions and I plan to investigate further with fc loss test, shocking, etc.

Its interesting that the suggestions are related to the condition of the water. This algae is not in the water (note that there is no algae growing below the water surface).

I'm curious, will the condition (chlorine content) of the water actually kill algae that is growing out of the water? Does the affect of the chlorine in the pool actually extend beyond the surface of the water?

 

[reebok]

the best way to kill that stuff (rescinding my first suggestion, repeating the second) is by getting a chlorine puck and rubbing it on there. the reason we're talking about overnight loss, etc. is because your water is out of balance (fc was too low) according to your first post, and we don't want you to start having bigger problems.