Green Pool Recovery

What causes it

Pools turn green when algae takes hold, usually after a stretch of low chlorine, unbalanced pH, warm weather, or a pool that's been left unattended for a while (a common one: coming back from a holiday to find the pool's turned on you). Poor water flow plays a part too. A pump that isn't running enough, or isn't circulating properly, leaves water sitting still for algae to take hold in rather than being constantly filtered and treated. High phosphate levels can also feed algae growth even when chlorine looks okay, since phosphates are a food source algae thrives on. Once algae establishes, it doesn't clear with a single shock dose; the water needs to be treated, tested, and re-treated in stages as the chemistry stabilises and the dead algae gets filtered out.

A filter that's overdue for attention makes all of this worse, since it can't clear dead algae and debris out of the water once treatment starts. See Filter & Media Changes if it's been a while since yours was serviced.

How We Recover a Green Pool

Every green pool gets the same structured process, not a single chemical dump and a wait and see.

1. 1.Scoop out any debris and give the pool a thorough brush, breaking up algae clinging to the walls and floor so the treatment that follows can actually get to it.
2. 2.Backwash the filter, clearing out anything already trapped so it's ready to filter properly once treatment starts.
3. 3.Bring the water balance to where it needs to be. The chemicals used in the next step only work properly once the water chemistry is in the right range.
4. 4.Shock dose the pool with chlorine and algaecide, then leave the pump running overnight so it keeps circulating and treating the water.
5. 5.If needed, add flocculant and leave the pump on recirculate for 6 hours, then the pump gets turned off, timed to let the flocculant settle everything to the pool floor.
6. 6.Come back the next day to vacuum to waste, which needs the pool full to work properly. This step sometimes needs repeating, since vacuuming to waste drops the water level and the pool needs refilling before another pass.
7. 7.Rebalance the water and add a phosphate remover (we use Nil Phos), so algae has less to feed on going forward, not just less algae in the water today.

How Long It Takes

How long a recovery takes depends on how far gone the pool is, but it's usually 3 to 6 days from the first visit to water that's genuinely clear and balanced, not just clear enough to look fine for a day before turning again. A pool caught early, still slightly cloudy rather than fully green, tends to sit at the shorter end of that range, while a pool that's been left for weeks with visible algae on the walls and floor takes longer, simply because there's more to break down and filter out. That's the standard that matters either way: the job's done when the water is actually recovered, whatever number of visits and days that takes for that specific pool.

What You'll Need to Do

A few things help the process along and matter for safety. Stay out of the pool until it's fully clear, since a green pool usually means low or no sanitiser, and where algae can grow, other organisms often can too. If flocculant goes in, the pump needs to be turned off when asked, since that's what lets everything settle to the floor instead of getting stirred back up. And keep the hose running to top the pool back up to full when asked, since vacuuming to waste especially drops the water level, and the pool needs to be full again before the process can continue. Turn it off once it's back up.

What to Know Before You Call

A green pool isn't just an eyesore. Green water usually means chlorine has dropped low enough for algae to take hold, and where algae can grow, bacteria and other organisms often can too, so swallowing contaminated water or getting it in a cut is where most of the health risk comes from. Green water also hides the pool floor, which is its own safety issue if anyone's tempted to swim before it clears. As a general rule, it isn't worth swimming in a pool until the green has genuinely gone and the water tests are holding steady, not just declared fine because it looks clearer today than yesterday. It's tempting to try and fix it yourself with a large chlorine dose from the local pool shop, but dumping chemicals into water that hasn't been tested and balanced first often wastes product and can make the imbalance worse rather than better. Draining the pool is usually not the answer either. It's expensive, and depending on the surface, draining a concrete or plaster pool incorrectly can damage the shell. In most cases the existing water can be brought back with a proper shock and filter process rather than starting from scratch. It also helps to know roughly how the pool got to this point before calling, whether that's a pump that's been off, a filter that hasn't been cleaned in a while, or simply a few weeks away with no one checking on it, since that context helps with diagnosing the cause alongside treating the symptom.

Why It's Treated as Urgent

Cooper's background is aircraft engineering and the fire service, both fields where you don't declare something fixed until it's actually verified fixed, and where a call marked urgent gets treated like one. A green pool gets the same treatment: it's queued ahead of routine visits, not behind them, rather than left to wait its turn.