Stubborn battle with greenish spots on walls and floor

nabril15

Bronze Supporter
May 22, 2011
395
Miami, FL
Hello all
My pool numbers look good, and the water is beyond crystaline. But for a week or so, I've been battling with "shadows" on the pool surface that are faint green; I will get pictures tomorrow. Neither a nylon brush nor a careful steel brushing takes them completely out. When I carefully brush them with the steel brush, they seem to fade away a bit, but I don't want to press too hard and I stop.
My CYA is at 30, and I've kept the FC between 9 and 11. Of course, Dorian has thrown rain at us here and there for a few days, but I've monitored the chlorine level daily.

Do I just "surrender" and SLAM? Even though the water is clear? Do I reach SLAM level and keep it there for 2-3 days, still doing oclt?
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
22,396
Laughlin, NV
You normally keep your FC at that level?

You keep a very low CYA level for your climate. Is the FC always above minimum when you test each day?
 

nabril15

Bronze Supporter
May 22, 2011
395
Miami, FL
No, cya is usually 40 or 50. I did 2 readings with new reagent, to make sure, and both read 30.
No, I normally don't keep FC that high, and I usually keep it toward the higher end of the appropriate range for the cya reading. Since the wall battle started, I've tried to keep the FC higher than the range but below slam. I just realized that I'm fairly close to slam for a cya of 30..
 

mikes112

Well-known member
May 28, 2019
45
New Jersey
Would you say the greenish spots are embedded in the plaster? I had similar situation and pressure washer was able to get them out, but of course my pool was drained at the time.
 
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nabril15

Bronze Supporter
May 22, 2011
395
Miami, FL
Would you say the greenish spots are embedded in the plaster? I had similar situation and pressure washer was able to get them out, but of course my pool was drained at the time.
hey mikes
yeah, I could say that. After brushing by hand with a metal brush, the stains remain. I didn't want to press too hard so as to not leave streaks. I guess that I could go down there with a pressure washer even with a full pool. The effect may not be quite the same, but the pressure will still get applied. Thanks for the idea. I will slam first.
 

mikes112

Well-known member
May 28, 2019
45
New Jersey
It's really the only way to get anything that's embedded in the plaster out, the plaster is like a sponge in some areas but that means the bonding agent in the plaster is starting to be eaten a way between the marble and white portland cement. I have this problem but in like 1 foot round areas in my pool but not the whole surface area and am experimenting with trying to fill in this porosity with out having to replaster. 0717190916a_Film3.jpg
 
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nabril15

Bronze Supporter
May 22, 2011
395
Miami, FL
I would suggest you follow the SLAM Process. May want to raise your CYA to 40 or 50 ppm to protect the FC better during the day. Adjust the FC levels appropriately.
I raised my cya to 40, and have run a slam for 3 days now in which every day I pass the test to stop; I even took out the light. My water was and is crystal clear, and oclt has equaled = 0 for the last 2; yet the green shadows/stains on the wall continue.
Do I need to find a pressure washer and explore that route? It sounds like it. I don't own one, and we all know how all of us feel about borrowing one...
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
22,396
Laughlin, NV
No on the pressure washer. It can easily damage your plaster.

So are we sure this is algae? Do you have trichlor puck you could put on the 'stain' for a few minutes and see if it changes?
 
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nabril15

Bronze Supporter
May 22, 2011
395
Miami, FL
No on the pressure washer. It can easily damage your plaster. So are we sure this is algae? Do you have trichlor puck you could put on the 'stain' for a few minutes and see if it changes?
thanks marty
I do have pucks, and I'll try that approach. Unfortunately, they are on walls as well, and at the bottom where floor meets the walls. But, I guess that would be a good start. I should leave the puck on top of one of the stains, and expect to see a whitened circle within a few hours or so, no?
 

nabril15

Bronze Supporter
May 22, 2011
395
Miami, FL
@mknauss and others
Marty.. I finally got around to doing the puck test. It is not easy to do since my blotches aren't so dark where the puck would leave a white circle; the blotches are faded and I circled 2 samples on the 2 pictures. I think that I saw the area under the puck be less green than before, but it's hard to tell; it might be a visual plazebo effect.

The majority of the blotches are on the walls and the curve at the bottom of the walls, so I cant leave the puck there.

What else can I do? I thought about maybe pouring 3 or 4 jugs of liquid chlorine so as to do a mega shock /slam. My current numbers, ta 70, cya 50, ch 250, fc was 12 yesterday - I've been maintaining the fc higher than the top of the range.
 

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mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
22,396
Laughlin, NV
If it is organic (algae), an elevated FC for a while should work. I would suggest keeping it at 9 or 10 ppm FC so you can test pH.

As the puck on them was not definitive, try a handful of Vitamin C tablets in a stocking crushed up and hold that on the stain for several minutes. See if it goes away or changes color.
 
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nabril15

Bronze Supporter
May 22, 2011
395
Miami, FL
If it is organic (algae), an elevated FC for a while should work. I would suggest keeping it at 9 or 10 ppm FC so you can test pH. As the puck on them was not definitive, try a handful of Vitamin C tablets in a stocking crushed up and hold that on the stain for several minutes. See if it goes away or changes color.
I would almost bet vitamin C tablets will clear it. I have a slight metal staining issue and the one in the deep end looks like yours.
I'm going to need a lot of vitamin C. Wow. I'm still laughing at the replies, but if 2 of you wrote it, it must be something that works. Thanks a lot.
 

nabril15

Bronze Supporter
May 22, 2011
395
Miami, FL
I have a sock with crushed vitamic c pills pressed against a wall curve; let's see what it does.
Today's numbers are fc 12, cya 60, ta 70 and ch 250. I brushed a decent amount of algae from some walls and the floor, but I don't want to add chlorine so that my fc can drop and I can measure ph.
I'm afraid that if I don't add chlorine, the algae will get out of control even though I'm above the range for my cya of 60.