Black Stains on Vinyl Pool Liner

No pool owner wants stains on their vinyl pool liner. Vinyl pool liners are used in both inground and above ground pools, and they’re susceptible to staining from chemical damage, organic materials and minerals. So, what do you do when you discover black stains on vinyl pool liner? Here are a few tips to bear in mind.

Black Stains on Vinyl Pool Liner

This post is a guide that should help you avoid and deal with black stains that often plague vinyl pool liners. It highlights how to identify the source of the stain and find effective solutions.

Black Staining

Black stains on your vinyl pool liner can originate from various sources and they fall into two main categories: black algae and metal staining. You need to identify the type of stain as that will inform the treatment required to correct the problem in your pool.

For instance, manganese, iron and copper may be introduced into your pool via source water. These metals can form oxides in chlorinated pool water, precipitating out of solution and result in stains on the pool liner. Eventually, you’re likely to notice black, gray or brown stains.

When the pool water pH is below 7, copper may also dissolve from the fittings in the plumbing. Copper may also be present in some algaecides, though most currently use copper in a complex or chelated form that remains in solution.

• An easy way to confirm the presence of metal staining is to treat a small portion of the stained area with a pH reducer that will dissolve the metals. If the stain can be removed in the process, that’s a sign that the staining results from metal deposits, and you can treat the remainder of the stain in a similar manner. Once you’ve gotten rid of the stain, you’ll need to take preventive measures by treating the pool water with a chelating or sequestering agent.
• If the pH reducer has no effect, then the staining is likely due to an organic source such as black algae. Black algae will often appear on the pool liner as a series of small black spots. To get rid of the stain, start by using a nylon brush to brush the spots and open up the coating.
• Next, test the pool water pH and reduce it to the lower limit of the normal operating range (7.2). That helps to improve the chlorine’s effectiveness. Your next step is to super chlorinate the pool before adding a dose of a quaternary type algaecide, following the manufacturer’s recommended dosage. Continue brushing the algae stains to maximize the penetration of the chemicals and once they’ve been killed, vacuum the dead algae. About 24 hours after superchlorination, add polymer algaecide according to the recommendations of the manufacturer. And once the stain has been removed, resume normal water balance and chlorination.

Bottom Line

Black stains can be tough to remove but with the tips mentioned, your pool should be clean and spotless in no time. The trick when dealing with black stains or any other type of stain is to identify the source so you can find the best remedy. And once the stain is removed, take proactive measures to prevent a recurrence — especially if you’re planning on covering your pool for the winter to prevent it from freezing.