Pool Troubleshooting /
How to Kill Algae in a Pool
Brush, vacuum, and clean the filter first, then treat the water exactly by label directions. Keep circulation strong and don’t swim until the pool is clear.
Archive date: this article was written for PoolSkimmer on Oct 23, 2026 and given the earlier archive date of Sep 20, 2026 so the blog reads as an organized archive. It was not published on that date.
Dealing with pool algae
The surest way to eliminate algae is to clear the buildup, put the water in motion and then sanitize it as the product label instructs. This means you will need to brush down the walls and floor, vacuum up any debris that has been loosened and give the skimmer and filter a good cleaning. Let the pump do its work as directed. And if the water is slimy, cloudy or green, it is not fit for swimming until it has been properly treated and is clear.
First steps for a green pool
Before you put more chemicals in the water, address the visible algae:
- Skim off any leaves or things floating on top.
- Give the corners, ladders, steps, floor and walls a thorough brushing.
- Work the algae loose so it can be vacuumed out of the way.
- Vacuum the bottom to stop dead algae from going back into circulation.
When using a manual vacuum, submerge the head and hose prior to making the connection. Take your time with overlapping passes to avoid churning everything back up.
The role of the pump and filter
Without good water movement, algae will have a field day. Proper circulation ensures the filter can trap dead particles and that your chemicals are distributed throughout the pool. Make sure the equipment is in order:
- With the pump off, empty the skimmer basket.
- Service the filter per the manufacturer’s instructions; backwash only if the type of filter calls for it.
- Maintain a high enough water level for the skimmer to function.
- Run the pump in line with what the equipment manual says.
Even after treatment, a filter that is clogged or underperforming will see to it that you still have an algae problem.
Which chemicals are effective?
Shock treatments and sanitizers will kill the algae, but they are most effective once you have finished with the brushing, vacuuming and filter work. Stick to products made for pools and adhere to the label.
There are some non-negotiable safety rules:
- Never mix chemicals or try to improvise with household cleaners and home recipes; they can make the water unsafe and complicate matters.
- Do not guess at the dose.
- Read the label and put on the appropriate protective gear when handling them.
Why does it come back?
Quick returns of algae are seldom a matter of water treatment alone. It could be due to:
- Insufficient circulation from the pump or filter
- A skimmer basket or filter in need of cleaning
- Debris left on the surface or floor
- Not enough brushing to dislodge algae from the pool surfaces
- Failing to remove dead algae before treating
Keeping up with regular maintenance makes the pool far easier to manage and staves off growth.
When the pool remains green
Should the water stay green despite your best efforts with the brush, vacuum and label directions, there may be something more to it than ordinary algae. Equipment or flow problems and water balance issues should be examined.
It is time to bring in a qualified professional if the pool is still cloudy post-treatment, the filter is clogging over and over, or the pump is acting up with noise or poor circulation. If there is reason to suspect a leak, damaged part or an electrical fault, have someone look at it. In the case of an electrical issue, do not attempt a repair and keep swimmers out of the water. Follow the proper manuals and safety protocols before anyone is allowed in the pool again.
Sources and further reading
- [Hayward: Weekly pool maintenance](https://www.hayward.com/maintenance/weekly-pool-maintenance)