Opening your pool takes an average of 4 to 8 hours spread across 1 to 2 weekends. Do not rush it: the water treatment takes time. Start early enough to be swimming in a perfect pool by early May.
Step 1: Remove and clean the cover
Remove standing water from the cover with a submersible pump or wet vacuum before opening it, so dirt does not fall into the pool. Clean the cover with cover cleaner, rinse, allow to dry, and store in a cool, dry place.
Step 2: Inspect filter and equipment
Put the installation back together in the reverse order of winterizing : multiport valve back on, drain plugs in and winter plugs out of the lines.
Check the sand filter for clumping. Inspect all hoses and fittings for cracks or loose connections: frost can crack pipes. Perform a thorough first backwash of at least 5 minutes.
Step 3: Start the pump
Start the pump carefully for the first time after winter. Let it run 30 seconds, then stop and check all connections for leaks. Bleed air via the filter bleed valve.
Step 4: Top up the water level
Fill to halfway up the skimmer opening. After filling, retest the water: the fill water chemistry differs from the pool water.
Step 5: Test and balance the water
| Parameter | Target |
|---|---|
| pH | 7.2 to 7.6 |
| Free chlorine | 1.0 to 3.0 mg/l |
| Alkalinity | 80 to 120 mg/l |
| Calcium hardness | 200 to 400 mg/l |
Correction order: alkalinity first, then pH, then shock treatment.
Step 6: Shock treatment
A shock treatment is always needed when opening. Add liquid chlorine or calcium hypochlorite in the evening to reach 10 mg/l free chlorine. Run the pump overnight and the following day. Backwash the filter the next morning.
After 24 hours add preventive algicide for extra protection in the first weeks of the season.
Zwemland Algi-stop 1 litre (algaecide)
Liquid algaecide to prevent and fight algae in pools, for preventive use and acute algae growth.
- Pros
- Liquid, prevents and fights algae
- Usable preventively and against acute algae growth
- 1 litre bottle
- Cons
- Does not fix poor water balance or too little chlorine
The pool is ready to swim when
- pH is between 7.2 and 7.6
- Free chlorine is between 1.0 and 3.0 mg/l
- The water is clear and blue
Recommended products for opening
At opening you need a fast-acting shock chlorine first to sanitise the water after winter. A complete startup kit gives you everything in one go.
Interline Shock 55 Chlorine Granules (1 kg)
Fast-dissolving chlorine granules for shock treatments and acute disinfection, suitable for hard and soft water. Use when opening and closing the pool and after heavy use.
- Pros
- Works within 24 hours
- Dissolves completely, no residues
- Effective against bacteria and algae spores
- Ideal first treatment at opening
- Cons
- Raises pH slightly, check pH after treatment
- Wait 24 hours before swimming
Want the complete spring startup kit with pH correction, algicide and test strips included?
Pool Maintenance Kit Small
Complete maintenance kit for small pools up to 2,500 litres. Includes all chemicals needed for a full season.
- Pros
- All opening treatments in one box
- Suitable for pools up to 2,500 litres
- Cheaper than buying products separately
- Cons
- Only suitable for small pools
- Not for larger pools above 2,500 litres
Open the pool when outdoor temperatures consistently exceed 15°C, typically late April to early May in Northern Europe. Do not wait too long: algae growth starts even at lower water temperatures, so opening earlier with a clean shock treatment is better than opening to a green pool. If you use a winter cover, check underneath it once temperatures start rising.
Can I treat the cloudy winter water instead of replacing it?
Yes, in most cases. Unless the water is severely contaminated (black, muddy or visibly foul), it is cheaper and faster to treat it than to replace it. Follow the step-by-step water treatment plan above: correct alkalinity first, then pH, then shock to 10 mg/l free chlorine and run the filter for 24 hours. Most winter water clears within a few days with this approach.
How long until the water is clear after opening?
With correct treatment, the water clears within 24 to 72 hours. Severely contaminated water can take 3 to 7 days. Backwash the filter daily during this period to remove the debris the filter is pulling from the water. If the water is still hazy after 72 hours, check that pH and chlorine are within range and consider adding a water clarifier.
