You want your neighbours green with envy at your sparkling pool – not the pool water itself! So, you’ve shocked your pool, but the water’s still green. Grrr! Now what?

Green pool water is caused by a bad chemical balance, usually something other than just low chlorine. So, let’s start with some chemistry, and the basic requirements for pool water to stay clear.

Chlorine. Algae will grow and make your pool green and cloudy, unless the water is sufficiently chlorinated.

Correct pH. For normal use, your pool’s pH should be around 7.5. When you shock the water,  it should be between 7.2 and 7.6.

Correct alkalinity. Stay within the right range of alkalinity (that’s the dissolved salts that keep pH stable). This makes pH and chlorine levels easier to maintain.

That’s the theory. But, like most theorems, they need to be executed well to achieve what you’re after. In this case, you want crystal clear water. So, if you’ve tried the usual methods, think broader.

• • Stabilizer

When you use tablets to supply chlorine, over time the levels of the stabilizer from the tablets (cyanuric acid) can become elevated and “lock up” the free chlorine molecules, so it’s not able to kill the algae. You need to dilute the pool with fresh water.

• • Phosphates

High phosphate levels also cause algae problems. Phosphate enters the pool via organic means, like leaching out of leaves or drifting there from fertilizer. This organic material keeps the algae well-fed. So, starve them out. Use a phosphate-removing product.