First off, balance your water, paying particular attention to pH. Secondly, check your filter system and clean if necessary. Turn on automatic cleaners to help stir things up.

For suspended green algae, shock the pool. Thoroughly brush off any algae that may be clinging to the pool surfaces.

The total alkalinity (TA) is a measure of how much of the alkaline substances there are in the water. In the swimming pool water, we are concerned with bicarbonate alkalinity, which should be between 80 ppm and 120 ppm.

When the total alkalinity (TA) is within this range, it prevents rapid pH changes and "stabilises" the pH level.

If the TA is too low, Marbelite and plaster walls will become etched, metals corrode, the pool's walls and floor can stain, the water can turn green, eyes burn and we can have pH bounce (pH rapidly going up and down, seemingly at random).

In the Southeast England, we have very hard water. This water is full of calcium and products that are very aggressive for your hot tub or pool. Not doing anything firs up your hot tub and pool equipment like cattle.

Those products will help you preventing this situation from happening.