I have been struggling with what will remove black mold from my silicone pool grout. Things I have tried thus far are: using a paint brush and applying liquid pool shock then scrubbing with a stiff bristle brush, cutting a 3” chlorine tablet and rubbing the affected area, distilled vinegar and a scrub brush. The areas affected are below the waterline so I have drained the water below before attempting each of these methods. Nothing has worked well or easily. Lastly my water chemistry is always in line and is monitored by a computer that adds in chlorine and acid as needed. Any suggestions would be greatly appreciated. Attached is a picture of one of the problem areas.
Black mold in silicone pool grout!
- Thread starter Sandfan1
- Start date
- Feb 6, 2015
- 7,789
- Pool Size
- 12300
- Surface
- Plaster
- Chlorine
- Salt Water Generator
- SWG Type
- CircuPool RJ-45 Plus
Welcome to TFP! 
Post a full set of current test results from one of the recommended test kits.
Test Kits Compared
FC
CC
pH
TA
CH
CYA
Water temp
Salt (if a SWG pool)
Chances are your chlorine level is too low to kill the algae and keep it away.
Also have a look thru Pool Care Basics
Post a full set of current test results from one of the recommended test kits.
Test Kits Compared
FC
CC
pH
TA
CH
CYA
Water temp
Salt (if a SWG pool)
Chances are your chlorine level is too low to kill the algae and keep it away.
Also have a look thru Pool Care Basics
- Jun 24, 2021
- 15,656
- Pool Size
- 29000
- Surface
- Vinyl
- Chlorine
- Salt Water Generator
- SWG Type
- CircuPool RJ-60 Plus
Welcome to TFP!!! 
You have a perplexing situation.
Really hard to tell from the picture, almost looks like grout is missing...can you post a full set of chemical results? pH, FC, CC, TA, CH, CYA? Thanks.
The black algea will take hold in weak grout areas. The water chemistry causes the weak grout that the black algae finds small cracks to grow in. Need to see where you are on chems.
Many have had good luck using 3" pucks rubbing the edge into the grout directly, and scrub with a wire bristle brush. Obviously use rubber gloves.
The only thing that will get this is chlorine and time:
www.troublefreepool.com
You have a perplexing situation.
Really hard to tell from the picture, almost looks like grout is missing...can you post a full set of chemical results? pH, FC, CC, TA, CH, CYA? Thanks.
The black algea will take hold in weak grout areas. The water chemistry causes the weak grout that the black algae finds small cracks to grow in. Need to see where you are on chems.
Many have had good luck using 3" pucks rubbing the edge into the grout directly, and scrub with a wire bristle brush. Obviously use rubber gloves.
The only thing that will get this is chlorine and time:
Black Algae
This guide provides a step by step procedure for eliminating black algae in your concrete or gunite pool. Read full post here.
www.troublefreepool.com
I will test my pool and get back with those numbers. Right now the only 2 numbers I know immediately is my ph is 7.4 and my chlorine/ORP is always at 650mV as these are kept I line by my Hayward Sense and Dispense system.Welcome to TFP!!!
You have a perplexing situation.
Really hard to tell from the picture, almost looks like grout is missing...can you post a full set of chemical results? pH, FC, CC, TA, CH, CYA? Thanks.
The black algea will take hold in weak grout areas. The water chemistry causes the weak grout that the black algae finds small cracks to grow in. Need to see where you are on chems.
Many have had good luck using 3" pucks rubbing the edge into the grout directly, and scrub with a wire bristle brush. Obviously use rubber gloves.
The only thing that will get this is chlorine and time:
Black Algae
This guide provides a step by step procedure for eliminating black algae in your concrete or gunite pool. Read full post here.
Possibly coming from behind the tile.
Why did you use silicone grout?
Why did you use silicone grout?
You could have 650 orp and still have low FC. You should still test FC with a test kit.
I’ll be honest, silicone isn’t good for pool use. Stuff always makes its way behind it and does that, even in bathrooms and kitchens. I’d recommend peeling it out, and see if you can remove the film left by it with some abrasive.
But separately the algae is caused by under chlorination. If you are using ORP, it’s pretty common to not be very accurate especially in the presence of CYA/stabilizer. You can try the TFP-SLAM process on it, but you’ll need a more reliable method of testing the water so the recommended test kit (TF-100 would be needed.
From what I can tell it looks like it is in the surface and not coming from behind. The tile is glass so when I look from the side it’s on the top on all the way to the back. I personally didn’t choose silicone, it’s suppose to be for pools and spas and it says resistant to mold
! It’s what the pool installer said was best given our winters.If I remove the silicone grout and redo it, what grout material would you recommend?
- Jun 24, 2021
- 15,656
- Pool Size
- 29000
- Surface
- Vinyl
- Chlorine
- Salt Water Generator
- SWG Type
- CircuPool RJ-60 Plus
That article describes using silicone grout on fiberglass pools. Is there a specific reason for that? Silicone tends to be really hard to remove. Perhaps fiberglass shells are not as rigid as gunite and so they need some flexibility? I’d expect the thin set to also need flexibility if that was the case.Waterline Tile Installation - Further Reading