A green pool means algae has taken over, usually because sanitizer levels dropped, the pump was not running long enough, or the filter could not keep up. It looks alarming, but most green pools can be brought back without draining.
Why pools turn green
Algae spores enter every pool from wind, rain and swimmers. Sanitizer normally kills them before they can grow. When chlorine runs low, from heat, heavy use, a storm or a missed week, algae can bloom in a few days. Poor circulation and a dirty filter make it worse because water is not moving through the system and getting treated.
How a cleanup usually works
- Remove debris: leaves and sludge are skimmed out so chemicals are not wasted on them.
- Balance the water: pH and alkalinity are adjusted so sanitizer works effectively.
- Shock the pool: a large dose of chlorine kills the algae.
- Brush everything: walls, floor and steps are brushed to break up algae and expose it to the shock.
- Run the filter continuously: dead algae is filtered out, and the filter is cleaned often during the process.
- Vacuum: settled algae is vacuumed, sometimes to waste, so it does not go back through the filter.
- Repeat as needed: heavier blooms may need more than one round of shocking and brushing.
How long it takes
A light green pool can often be cleared in a day or two. A pool that has been dark green or black for weeks may take several visits over a week. The water usually turns cloudy blue before it turns clear, which is a normal part of the process as the filter catches up.
When draining is considered
Draining is rarely the first choice. It may be suggested if the water has very high levels of dissolved solids or stabilizer, or if the pool has been neglected so long that it is full of decaying debris. Draining has its own risks, especially for some pool types in high groundwater areas, so it should be done by someone who knows how to do it safely.
Questions worth asking
- How many visits do you expect this to take?
- Is the price fixed, or based on chemicals used?
- What caused the bloom, and how do we keep it from coming back?
- Does the filter need to be cleaned or replaced as part of this?
Keeping it clear afterward
Once the water is clear, steady sanitizer levels, enough daily pump run time and a clean filter keep algae from coming back. Many owners set up regular service after a cleanup so the pool does not slip again.
