Black Algae or......??

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michmosh

michmosh

0
Jul 26, 2014
15
Longwood,FL
Had our pool re-surfaced just over a year ago with a pebble finish. Of late there is a very dark area only around the drain, seems to have gotten worse.
It feels kind of rough. Doesn't brush off. Hard to clearly examine it in 8 feet of water.

Could this be black algae? Something going wrong with pool finish? Something else?

We are going to drain 1/2 of the water in the next month or so (high CYA - separate problem), that will make that area more accessible since water will be 4ft deep. What is the best way to determine the issue? What would indicate algae?

Having to keep the chlorine high because of high CYA, would that damage the finish? Assuming chlorine is heavier than water, could it accumulate at the drain due to the grading of the pool and would it be damaging in any way?

Really hoping it's something we can address without calling the guy who did our pool surface.

Thanks!!!
 
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Would you mind posting full set of test results and what you used to get those results?

Algae (of all types) are caused my a lack of FC based in your CYA. The higher the CYA, the higher FC you need, so your CYA issue is directly related to getting black algae. Take a look at this chart: http://www.troublefreepool.com/content/128-chlorine-cya-chart-slam-shock

To determine the source of your stain, you can test the stain by putting a vitamin C tablet on it for 30 seconds, it if lightens then you have a metal stain. You can test it by putting a chlorine puck on it (don't leave it on too long as it is acidic) if it lightens you have an organic stain.

Post some pictures, too and it will help us visualize the stains.
 
I saw your other post... is your CYA is still at 300? If so your recommended FC level is too high to maintain and will be extremely difficult to battle black algae (if this indeed your problem).

You should look into have water trucked in so you can get your CYA down to between 30 and 50.

According to pool math your recommended FC range (based on a CYA of 300) is between 22 and 33 and your shock level is astronomical.

What is your fill water test results (including CYA since your said your well water is treated with stabilized chlorine).

BTW, if your stains are metal (like iron from your fill water), high FC levels makes metal staining worse.
 
kcindc said:
I saw your other post... is your CYA is still at 300? If so your recommended FC level is too high to maintain and will be extremely difficult to battle black algae (if this indeed your problem).

You should look into have water trucked in so you can get your CYA down to between 30 and 50.

According to pool math your recommended FC range (based on a CYA of 300) is between 22 and 33 and your shock level is astronomical.

What is your fill water test results (including CYA since your said your well water is treated with stabilized chlorine).

BTW, if your stains are metal (like iron from your fill water), high FC levels makes metal staining worse.
Click to expand...

Thanks for the reply. When we re-surfaced last year we used the raw well water with some sort of metal control filter on the end of the hose. Yes, CYA is still high, not sure it's 300 still as we have had a lot of rain all summer but I am sure it is pretty close to that. I don't check it regularly because it's not going to come down to a manageable amount without a drastic measure such as trucking in water (which is the plan asap) so at this point I would just be wasting reagent to get an off the chart reading anyway. I have been keeping the FC at 16-20 ppm. And yes, shock level is a ridiculously high number that I haven't attempted to attain because I can't imagine getting in that water or that it could be good for the pool surface or equipment. And since it hasn't been "shocked" that is what made me question the black mark being black algae. But what you are saying abut high FC and metal staining makes a lot of sense too.

Surprisingly, when I brush the pool nothing algae-like gets stirred up and it looks great and is clear and blue. I have attached a photo so you have a visual, but I don't have an underwater camera so it's not the best quality from above the water. After googling pictures online of black algae, it doesn't really look like that (to me).

I think this whole CYA mess started after we had the pool re-surfaced. The contractor added the start up chemicals and when I look back at the pool store tests we had done that I saved we were already at 100 a month after the re-surface. No one at the pool store ever mentioned it or told us this could be problematic. But yeah, I think he must have added way too much stabilizer.

IMG_4280.jpg
 
Hard to say without test results, it's just guesswork.. Have you tested to see if it's a metal stain? Placing a puck directly on the stain for just a few minutes will noticeably lighten it if it is metal.
 
Has anyone started a betting pool yet since we're all just guessing at this point.

Here's my guess - mottled aggregate.

When PebbleTec plaster is applied, the drain (ie, the lowest point in the pool) is typically the last place smoothed over by the resurfacing crew. They stand on their stilt shoes until the plaster near them has dried then they hop out of their stilts and use their lathes to smooth out the aggregate near the drain. Aggregate mix is never perfect and never totally uniform and it's entirely possible that larger or darker stones in the aggregate settled out near the drain.

As well, the final acid wash to expose the aggregate is critical to color uniformity as an uneven plaster relief can cause a mottled appearance as well. The drain is where all of the spent acid and loose aggregate settles and so it's very easy for that area to be uneven if the acid washing fluid isn't pumped out sufficiently fast enough.

Perhaps, over time, your pool water has removed some plaster there as well and some darker aggregate or the old surface underneath is now more prominent.

I'll wager a bottle of beer and some old Leslie Pools test strips on my guess ;)



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SunnyOptimism said:
Has anyone started a betting pool yet since we're all just guessing at this point.

Here's my guess - mottled aggregate.

When PebbleTec plaster is applied, the drain (ie, the lowest point in the pool) is typically the last place smoothed over by the resurfacing crew. They stand on their stilt shoes until the plaster near them has dried then they hop out of their stilts and use their lathes to smooth out the aggregate near the drain. Aggregate mix is never perfect and never totally uniform and it's entirely possible that larger or darker stones in the aggregate settled out near the drain.

As well, the final acid wash to expose the aggregate is critical to color uniformity as an uneven plaster relief can cause a mottled appearance as well. The drain is where all of the spent acid and loose aggregate settles and so it's very easy for that area to be uneven if the acid washing fluid isn't pumped out sufficiently fast enough.

Perhaps, over time, your pool water has removed some plaster there as well and some darker aggregate or the old surface underneath is now more prominent.

I'll wager a bottle of beer and some old Leslie Pools test strips on my guess ;)



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Click to expand...



Hmmm....you could be right. That area does feel rougher than the unaffected surrounding areas. When the pool is drained down I guess we'll know more, hopefully. I can certainly try the puck test too and see if it lightens. One person said that would indicate metal and another said organic? Just seems odd that if it was staining or algae why only at the drain? Which is why your explanation about application sort of makes sense.

Our pool contractor is kind of a jerk and I am not looking forward to dealing with him. He will probably say that it is normal and color variations are part of the look. Which is true for this product I know, but the drain area being black in a blue pool is not normal and not the look I am going for. And it wasn't like that before.

You might be correct, but even if not, you can keep the Leslie's test strips!):cheers:
 

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TriChlor pucks can lighten or remove metals because they acidic. They lighten organics because they contain chlorine.

You're going to need both a trichlor puck and a vitamin C tablet to make a determination. Use the trichlor tab first and if you see it work then use a vitamin C tablet in a different spot. If the vitamin C fails, then it's organic. If the vitamin C works as well, then it's most likely a metal. If both fail, then you might have some kind of mottled plaster.

Yeah, PBs don't like dealing with mottled plaster because the only solution is to drain the pool and chip out the affected area. And, you need a PebbleTec crew that knows what the heck they are doing otherwise it's not going to match and it will look like a patch-job.

Here's hoping I'm wrong.....


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SunnyOptimism said:
TriChlor pucks can lighten or remove metals because they acidic. They lighten organics because they contain chlorine.

You're going to need both a trichlor puck and a vitamin C tablet to make a determination. Use the trichlor tab first and if you see it work then use a vitamin C tablet in a different spot. If the vitamin C fails, then it's organic. If the vitamin C works as well, then it's most likely a metal. If both fail, then you might have some kind of mottled plaster.

Yeah, PBs don't like dealing with mottled plaster because the only solution is to drain the pool and chip out the affected area. And, you need a PebbleTec crew that knows what the heck they are doing otherwise it's not going to match and it will look like a patch-job.

Here's hoping I'm wrong.....


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Click to expand...

I am going to hope this is staining! How long do I leave the puck/vitamin C sitting on the stain before I determine it's not working? Should something start to occur pretty quickly if it's going to? Don't want to leave that puck on there too long.

Thanks again!!

- - - Updated - - -

tim5055 said:
If only we had a way to determine this before we deal with people.....
Click to expand...

You are so right! First he'll look & squint and say he doesn't see anything wrong, then getting him to take responsibility for it will be another whole can of worms!
Hoping not to have to call him. :(
 
Just to add closure to this thread, it was fortunately not the pool finish wearing away. It was staining of some sort, but I can't be sure of what nature because neither the vitamin C nor the puck caused any change. While draining the water down we used a piece of PVC to pour some acid on the stain and with a metal bristle brush and some elbow grease it came off.

Thank you to everyone who posted for taking the time to reply and assist! :handshake:
 
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