Pool Turned Green? Here's the Fix.

Before you shock, get your pH to 7.2. Chlorine works best at lower pH. If your pH is 7.8 or higher, about 40% of the chlorine you add will be wasted.

Add muriatic acid to lower pH. About 1 quart per 10,000 gallons lowers pH by 0.2. Run the pump for an hour, then retest.

This step alone can double the effectiveness of the shock treatment that follows.

Brush the walls, floor, steps, ladders, and every surface. Algae clings to surfaces and forms a protective layer. Brushing breaks that layer and exposes the algae to the chlorine you're about to add.

Pay extra attention to corners, behind ladders, and anywhere with poor circulation. These are where algae hides.

This is not a regular weekly shock. You need to raise free chlorine to at least 10 ppm for a light green pool, 20 ppm for medium, and 30 ppm for dark green or black water.

Do NOT use stabilized shock (dichlor). It adds CYA, which you don't want during a heavy shock treatment.

Do not turn off the pump until the water is clear. Run it continuously. The filter is catching dead algae particles, and the circulation is distributing the chlorine to every corner of the pool.

The water will likely go from green to cloudy/milky. That's a good sign. It means the algae is dying and the filter is working.

Your filter is going to get overwhelmed with dead algae. Check filter pressure every 6 to 8 hours. When pressure rises 8 to 10 psi above normal, clean it.

For a bad green pool, you may need to clean the filter 3 to 4 times during recovery. This is normal. If you don't clean it, the filter stops working and the pool stays cloudy.

Test chlorine every 8 to 12 hours. If FC drops below 5 ppm before the water is clear, add more chlorine. The algae is consuming it, and you need to keep ahead.

Once the water is clear (you can see the bottom), vacuum any debris from the floor and rebalance all your chemistry. Don't swim until FC drops back below 5 ppm.