Vinyl Liner Has Dark Stains On Bottom

by Greg
(Detroit, MI.)

I have an above ground pool that is partially sunken into the ground.

The bottom has developed dark stains that seem to be coming from under the liner.

They do not scrub off or respond to shock treatments or algae treatments. (Black and normal)

I have heard that black algae can exist under the liner and stain through it.

Is this true, and if so, how do you treat it?

If I have to replace the liner, can I treat the sand underneath the liner to prevent this from re-occurring?

Thanks for the question Greg

Before we jump to conclusions, we need to see what the stains are.

You can crush some Vitamin C tablets in a sock and put them on the stain for about an hour. If the stain lightens up or is gone, it's a metal stain.

Go here to learn how to remove metal stains:

Pool Liner Stained From Acidity Too High

Next, you can put a Trichlor puck on the stain.

If that lightens it up or removes the stain, it's organic. This can be treated with a good pool shock and an adequate chlorine level.

Black algae in a vinyl pool is possible, but not very likely.

Black Algae

The stain could possibly be a fungus and growing under the vinyl liner.

To treat a fungus would mean getting a fungicide and putting that under the liner.

This means draining the pool to apply the fungicide and installing a new liner.

There is a foam that you can possibly use, but you'll want to check with the manufacturer of your pool to see if it's possible.

Here's a post I answered about that:

Inground Pool Steel Walls..Should You
Use Foam On The Walls?

This was for an inground pool.

Hope this helps and good luck with your pool.


New Question: Wrinkles And Black Areas On An Inground Vinyl Liner Pool

By: Alta
From: Cleveland, Ohio
Date: June 22, 2011

We have an 18 x 36 inground vinyl liner pool.

A DE filter liner is 3 years old this year.

We have wrinkles in the shallow end and black spots deep and shallow ends which seems to be under liner.

Any solutions?


By: Robert
Date: June 22, 2011

Thanks for the question Alta

I have actually answered very similar questions in the following posts:

Black Stains On My Above Ground Saltwater Pool

Vinyl Liner Has Dark Stains On Bottom

Black Algae

Black algae normally doesn't occur on vinyl pools, it can, but unlikely.

Brown Algae Won't Come Off Of A Vinyl Liner

You first need to see whether the black spots are either organic or metal. If it's organic you'll need to do an ascorbic acid treatment.

The link above gives details on how to do that treatment and how to see if the black spots are metal.

Here are some other posts about wrinkles in a liner:

How Do I Get Out Wrinkles In Aboveground 24' Expandable Liner

Swimming Pool Liner Wrinkles and Black Algae Problems

These are the links you need for troubleshooting your problem.

Due to space and similarity, I'm merging your questions with this one:

Vinyl Liner Has Dark Stains On Bottom

If you have any more questions or comments, you can find this link on the Q&A page in the "Pool Liner" category.

Swimming Pool Questions and Answers

Hope this helps and good luck with your pool.


Click here to read or post comments

Return to Vinyl Swimming Pool Liners.

Dirt Ring Around Sides Of The Swimming Pool At Water Level

Dirt at the water level. The water tests are good, but have a dirt ring around the top of the swimming pool water level.

What could cause this? I also have a lab that loves to swim.

Thanks for the question

The simplest answer would be you have excess dirt in your swimming pool that your filtration system is not getting out. I would first check your swimming pool filter system.

Swimming Pool Sand Filters

This is a good starting point. Without knowing which kind of system you have I cannot give an exact answer. Check your skimmer baskets and pump basket to be sure they are clean. Keep the pool water level between 1/3 - 1/2 up from the bottom of the skimmer.

This is to ensure there's proper suction going from the skimmers to the pool pump motor. Also be sure you have a working swimming pool pump motor and that's it's properly sized for your pool. You can check the horsepower on the plate that is attached to the pump motor.

Most pool pump motors are either under-sized or over-sized. If you have an open area with lots of dirt it may be beneficial to grass it in to keep the dirt down. And maybe give your dog a bath before allowing it to swim.

Click here to read or post comments

Return to Vinyl Swimming Pool Liners.

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