It could be just one small pot on the water line on steps or on the floor of the pool.
Dark spots on vinyl pool liner.
Step 2 check the ph levels of the pool with the test kit.
Then scrub the spots again.
If the stain is old or excessive then the pool may have to be shocked to remove the stain.
Brush every black algae spot with a steel bristle brush to remove the protective layer.
If your pool has a dark surface you may need to skip this step as it could cause discoloration.
Mineral and metal stains.
The stain colors range from yellow to brown to black.
Beware this works great on plaster pools but don t try this to remove stains on a vinyl pool because it could remove the liner pattern.
Repeat until the black spots go away.
The spots are black or blue green with raised heads not free floating.
Black algae will often appear on the pool liner as a series of small black spots.
Jack will be vinyl liner blue stuff a powerful sequestrant that prevents and removes stains on vinyl pools.
And while a vinyl pool is not nearly as susceptible to algae if you happen to notice an infestation a softer bristled brush can be used.
Vinyl liners can stain in localized areas and spread throughout the pool surfaces.
If you have a vinyl lined pool do not use a wire brush as this can tear the liner shock or super chlorinate the pool using granular chlorine also known as calcium hypo chloride.
If the stain lightens from a small application of chlorine on it the stain is organic in nature.
Too much copper iron calcium or salts can all result in vinyl liner staining or marks.
Algae require a high ph level in order to thrive so you should find that the ph levels are a bit high.
In most cases this is all that is needed with vinyl pool liners.
To get rid of the stain start by using a nylon brush to brush the spots and open up the coating.
Too much copper usually results in blue green staining while iron results in.
For metal stains either stain solution 1 the iron cobalt spot etching stuff or 2 the copper scale stuff may be indicated depending on the metals discovered.
Nylon brushes will not work.
The size location and color are important to identify the cause of the pool stain so you can properly identify and stop the source.
If you have black or grey cloud like stains on the floor of your in ground vinyl liner they are most likely caused by bacteria that is living in the ground under your pool.