Green Pool Recovery Guide
Recovering a green pool is not overly complex, however following the correct process is essential. These steps are designed to kill algae, remove the nutrients feeding it, and restore your pool water to a clear, healthy condition.
Why Pools Go Green and How This Process Fixes It
Algae blooms occur when three things are present: algae spores, nutrients (phosphates), and inadequate sanitiser levels. The recovery process works by attacking all three:
- Chlorine kills the algae directly
- Lowering the pH makes the chlorine far more effective
- Algaecide destroys any remaining live algae
- Phosphate remover eliminates the algae's food source to prevent it from returning
- Clarifier and flocculant bind dead algae particles so your filter can remove them
The order of these steps matters. Skipping ahead or changing the sequence can slow the recovery and may require additional treatments.
| Problem | Most likely cause | Fix |
|---|---|---|
| Pool still green after shocking | pH too high, or not enough chlorine | Lower the pH, re-check chlorine dosage |
| Pool cloudy but blue | Fine dead algae particles suspended in water | Add clarifier or apply flocculant |
| Algae keeps returning | Phosphates present, or filter not cleaning effectively | Add phosphate remover, clean filter regularly |
| Green water not improving after 48 hours | Filter not running continuously, or undersized pump | Set pump to Manual mode, check pump sizing |
| Dead algae settling but can't vacuum it | No waste bypass, cartridge filter clogging | Clean cartridge frequently, use clarifier instead of floc |
| Pool clear but water has a green tint | Metals in water (copper/iron), not algae | Test for metals; this requires a metal sequestrant, not chlorine |
Remove from the pool:
- Robotic pool cleaners
- Suction cleaners
- Pool toys
- Floating devices
- Thermometers
- Any other removable accessories
Next, remove as much debris as possible using a leaf scoop, rake, or shovel:
- Leaves
- Twigs
- Branches
- Dirt
- Any other organic matter
Brush these areas:
- Walls
- Floor
- Steps
- Corners
- Behind ladders where possible
Vacuum the pool:
Even if you cannot see the bottom of the pool, perform a vacuum. This is commonly referred to as a "blind vacuum" and is an important step in removing settled debris and algae.
- Sand or media filter: Vacuum to waste
- Cartridge filter with waste bypass valve: Vacuum to waste using the bypass
- Cartridge filter without waste bypass: Vacuum normally through the filter. Be prepared to clean the cartridge regularly throughout the recovery process, as it will collect large amounts of dead algae and block the cartridge
For every 50,000 litres of pool water, add either:
- 2 kg of stabilised granular chlorine, or
- Three 15 litre drums of liquid chlorine
If using stabilised chlorine: Pre-dissolve it in a clean bucket of pool water before slowly pouring it in front of the return jets.
If using liquid chlorine: Slowly walk around the perimeter of the pool while pouring it evenly into the water.
Allow the filtration system to circulate the chlorine for 30 minutes.
Per 50,000 litres:
- 1 litre of hydrochloric acid
Lowering the pH improves the effectiveness of chlorine, allowing it to kill algae much more efficiently.
Allow the pool to circulate for another 30 minutes before moving to the next step.
- 1 litre of algaecide
- 1 litre of phosphate remover
The algaecide helps destroy any remaining live algae. The phosphate remover eliminates phosphates from the water, which are the food source for algae. Removing phosphates helps reduce the chance of the algae returning after treatment.
Continue running the filtration system continuously.
- If possible, vacuum to waste to remove the dead algae from the pool completely
- If you are using a cartridge filter without a waste bypass, clean the cartridge whenever the water flow begins to reduce or the filter pressure increases
- During severe green pool recoveries, this may be several times per day
- 500 mL of liquid clarifier
The clarifier helps bind together the tiny dead algae particles, making them easier to vacuum and for your filter to remove.
Continue running the filtration system continuously.
Continue filtering the pool continuously for the next 24 to 48 hours.
At this stage, if you have a sand filter, applying a flocculant treatment is recommended. After applying the flocculant, allow the particles to settle to the bottom of the pool before carefully vacuuming them directly to waste.
This procedure can only be performed if you have:
- A sand or media filter, or
- A cartridge filter fitted with a waste bypass valve
If your cartridge filter does not have a waste bypass, you will need to use a portable submersible pump to vacuum the settled debris directly to waste, or continue to use a clarifier in place of the floc.
Expected Recovery Time
Every pool is different depending on the severity of the algae and the condition of the filtration system. As a general guide:
- Green water should begin turning cloudy blue within 6 to 24 hours
- Most pools will recover within 24 to 72 hours, with severe cases up to 5 days
- Severe algae blooms may require additional brushing, vacuuming, chlorine and filter cleaning
Patience is important. Keep the filtration system running continuously until the water is completely clear.
Run the pump 24/7
Keep the pump running 24 hours a day during the recovery.
Maintain water level
Maintain the correct water level, especially when vacuuming to waste.
Clean filters regularly
Clean cartridge filters regularly or backwash media filters whenever required.
Avoid swimming
Avoid swimming until the water is clear and chlorine and pH levels have returned to safe ranges.
Maintain chlorine levels
Maintain the chlorine levels throughout the entire process.
Replace cartridge upon completion
Replace the cartridge filter upon completion.
Empty baskets
Empty skimmer and pump baskets regularly.
Correct all chemistry
Upon completion, correct all necessary chemistry and maintain the correct levels.
- Undersized pump: A pump that's too small for your pool volume cannot circulate water effectively. Minimum ¾ HP is recommended for most residential pools.
- Old or damaged filter media: Sand in sand filters should be replaced every 5 to 7 years. Cartridge filters that are more than 2 years old may not filter effectively even after cleaning.
- Channeling in sand filters: If the sand has channelled (formed paths where water bypasses the sand), backwashing alone won't fix it. The sand may need to be replaced.
- Extremely high phosphate levels: Some pools may require a second dose of phosphate remover if levels are exceptionally high.
- Water age: If your pool water is more than 5 to 7 years old, dissolved solids can build up to levels that make it difficult to maintain clear water. In these cases, a partial or full drain and refill may be the most effective option.
Wear protective equipment. Always wear gloves and eye protection when handling pool chemicals.
Read product labels. Always read and follow the manufacturer's instructions on all chemical products.
Never mix chemicals. Add chemicals separately and never mix them together before adding to the pool. Mixing chlorine and acid directly can create dangerous gases.
No swimming. Do not swim during the green pool recovery process. Wait until the water is clear and chemical levels have returned to safe swimming ranges.
Remove equipment. Remove all pool cleaners, toys, and accessories before adding chemicals. High chlorine levels can damage these items.
Work in ventilated areas. When handling liquid chlorine or acid, ensure you are in a well-ventilated area and avoid breathing fumes.
Green Pool Recovery FAQs
Most pools will begin turning from green to cloudy blue within 6 to 24 hours. Full recovery typically takes 24 to 72 hours, though severe cases can take up to 5 days. The key factors are the severity of the algae, your filtration system, and how consistently you follow the steps.
Vacuuming to waste removes dead algae and debris directly from the pool without passing it through your filter. This prevents your filter from becoming overloaded and sends the waste straight out of the pool.
Yes. For every 50,000 litres of pool water, you can use either 2 kg of stabilised granular chlorine or three 15 litre drums of liquid chlorine. Both are effective. Liquid chlorine is poured directly into the pool while walking around the perimeter. Granular chlorine should be pre-dissolved in a bucket of pool water first.
If your pool is blue but cloudy after 48 hours, the cloudiness is usually caused by very fine dead algae particles suspended in the water. Using a flocculant (if you have a sand filter or waste bypass) or continuing with a clarifier will help bind these particles together so your filter can remove them.
During a severe green pool recovery, you may need to clean your cartridge filter several times per day. Clean it whenever the water flow begins to reduce or the filter pressure increases. Keeping the filter clean is one of the most important parts of recovering a green pool.
No. Avoid swimming until the water is completely clear and the chlorine and pH levels have returned to safe swimming ranges. High chlorine levels used during recovery can cause skin and eye irritation.
Yes. Continuous filtration is essential during the recovery process. The filter needs to constantly circulate the chemicals and remove dead algae particles from the water. Set your filtration system to Manual mode so it runs continuously until the recovery is complete.
A clarifier binds tiny particles together so your filter can catch them. It works continuously with your filter running. A flocculant binds particles together and makes them sink to the pool floor, where they must be vacuumed directly to waste. Flocculant requires a sand/media filter or a cartridge filter with a waste bypass valve.
Pools go green when chlorine levels drop too low and algae takes hold. Common causes include: pump not running long enough each day, heavy rain diluting chemicals, high bather load, debris (leaves/dirt) in the pool consuming chlorine, or simply forgetting to maintain chlorine levels. Once algae is present, it multiplies rapidly, especially in warm weather.
If you have questions during your recovery, our team is here to help. The more information you can provide, the quicker we can diagnose the issue.
1300 511 901 | support@mrpoolman.com.au
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Mr Pool Man. Complete green pool recovery guide. Follow each step in order for best results.