Black algae can ruin the pristine look of a pool. Black algae can form in either regular or salt water pools, and it often forms in the cracks of pool surfaces, especially in cool, shady areas. It sometimes creates a heavy, slimy layer. Although black algae doesn't have any effect on the clarity of water, it does make the pool appear to have black spots on its surface.
Brush the algae thoroughly with a stiff pool brush to “break open” the slimy layer. Failing to do this may prevent the treatment from working as chemicals won't be able to penetrate the algae as well.
Shut off the pool pump.
Pour algaecide over the black algae according to the directions on the bottle and leave it overnight.
The next day, brush away and discard all the dead algae spots.
Repeat the process if you continue to see some black algae spots.
Restart the pool pump for circulation and adjust the pool's salt levels.
Make sure you maintain proper salt water chlorination levels as it helps kill bacteria and prevent black algae from growing back.