Gravel fill coming in through my steps!? (in-ground pool)

mjc123

Well-known member
Jul 20, 2018
114
Halifax, NS (Canada)
Pool Size
18500
Surface
Vinyl
Chlorine
Salt Water Generator
SWG Type
Hayward Aqua Rite (T-15)
Hey all, ever since I bought my house (along with the pool) back in 2018, there have been what I thought were black stains on the steps - little black dots basically. I've tried scrubbing them with a Magic Eraser but had no luck making them disappear; and other than how it looks, they don't bother me. So this summer I put a mask on and looked up close for the first time, and as far as I can tell, the gravel that must be packed against the back of the steps are poking through all over the place - and yet, the pool isn't leaking at all. It's extremely difficult to take a picture or video, but I'll do my best.

From a distance:

A bit closer:

There's also these "bumps" where it looks like there's point pressure pushing out:

This might give a slightly better view, but still hard to really see:

Anyway, has anyone come across anything similar? Perhaps I'm wrong about it being gravel poking through, but I'm not sure what else it could be. I have a hard time believing the gravel could be putting that much pressure on it, but then again, freeze-thaw cycles here are pretty crazy so perhaps it's that? idk. Like I said, pool isn't leaking, so it's really just an aesthetics issue at this point.
 
Hey all, ever since I bought my house (along with the pool) back in 2018, there have been what I thought were black stains on the steps - little black dots basically. I've tried scrubbing them with a Magic Eraser but had no luck making them disappear; and other than how it looks, they don't bother me. So this summer I put a mask on and looked up close for the first time, and as far as I can tell, the gravel that must be packed against the back of the steps are poking through all over the place - and yet, the pool isn't leaking at all. It's extremely difficult to take a picture or video, but I'll do my best.

From a distance:

A bit closer:

There's also these "bumps" where it looks like there's point pressure pushing out:

This might give a slightly better view, but still hard to really see:

Anyway, has anyone come across anything similar? Perhaps I'm wrong about it being gravel poking through, but I'm not sure what else it could be. I have a hard time believing the gravel could be putting that much pressure on it, but then again, freeze-thaw cycles here are pretty crazy so perhaps it's that? idk. Like I said, pool isn't leaking, so it's really just an aesthetics issue at this point.
Try sprinkling some calcium hypochlorite (commonly packaged as Shock) on those spots. It may remove those spots from the fiberglass. Don't panic over the tiny amount of calcium that will be added to the pool. It needs to be cal-hypo, not sodium-dichlor which is also packaged as shock. Both are available in 1# bags.
 
Try sprinkling some calcium hypochlorite (commonly packaged as Shock) on those spots. It may remove those spots from the fiberglass. Don't panic over the tiny amount of calcium that will be added to the pool. It needs to be cal-hypo, not sodium-dichlor which is also packaged as shock. Both are available in 1# bags.
They're underwater - won't the shock just disperse? Or are you suggesting I drain 4 feet of water first? not worried about calcium - last time I checked it was < 25ppm. FWIW the steps are not fiberglass but some sort of plastic. In any case I'm certainly willing to try it - though I'm not convinced they're just stains; but at least if I do drain the pool a bit I'll be able to get a better look. hard to take macro photos underwater with an iphone
 
They're underwater - won't the shock just disperse? Or are you suggesting I drain 4 feet of water first? not worried about calcium - last time I checked it was < 25ppm. FWIW the steps are not fiberglass but some sort of plastic.
No, just sprinkle it over the spots. It dissolves slow enough to reach the bottom of a 10-foot deep pool. Never used it deeper.
 
Cobalting or Black Dots are miniscule air holes that develop when the gel coat is applied.

Black spots, also known as cobalting, in fiberglass pools can be caused by a few things, including:
Osmosis: Also known as "Black Plague," osmosis occurs when air or contaminated water seeps through the pool's lining, causing blisters to form on the surface.

Black spots are the result of a weakened gel coat and the breakdown of the minerals within your fiberglass surface. As your gel coat weakens and the fiberglass breaks down, tiny pinholes will form on its surface, where this sludge-like black substance surfaces.


Most likely to be cobalt staining. Cobalt is used as one of the chemicals in some fiberglass resin. A reducing agent, such as ascorbic acid or oxalic acid might help temporarily, but the stains are likely to reappear. Using a higher calcium level and a sequestrant might help reduce reoccurrences. However, I think that the pool would need to be refinished with a high quality gelcoat to prevent future reoccurrences.
 
Black cobalt stains, also known as "cobalting", are a common problem in fiberglass pools and spas:

They appear as dark, ink-like splotches or black spots on the surface of the fiberglass.

The stained area may also have a slight bump.

They are caused by a chemical reaction between the water and the fiberglass.

Water penetrates pinhole gaps in the gelcoat and reacts with the resin beneath, creating crystallized areas of black discoloration.

Older fiberglass pools with a high cobalt content in the resin may leach cobalt into the pool water.




 
FWIW the steps are not fiberglass but some sort of plastic.
The steps are typically fiberglass covered by a top coat of plastic.

The top coat (sometimes called a gelcoat) can get defects like pinholes and blisters.

The black is probably cobalt from the fiberglass.

You would need to remove the top coat and refinish it with a suitable material.
 
Thanks @JamesW - those pictures do look an awful lot like mine. removing the top coat and refinishing it is not really a practical solution for something that is ultimately just cosmetic in this case. I'm not sure I like the idea of draining the entire pool until such time it makes sense to replace the liner as well; not to mention the labour involved in trying to remove the top coat in the first place. I might try digging through those posts you linked in greater detail to see if someone has any concrete chemical solutions
 
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