Opening the pool is one of the best days of the year, and also the moment when the water is most likely to go wrong. After months under a cover, chlorine is gone, the water level is off and the equipment has been sitting dry. Do it in the right order and most pools are ready to swim in within a few days.
When to open
Open earlier than you think. Once water temperatures rise above about 65°F (18°C), algae starts growing quickly, and an uncovered, chlorinated pool is much easier to keep clear than a covered one with no chlorine at all. Opening a couple of weeks before you plan to swim also gives you time to fix any problems.
Step 1: Remove and clean the cover
Pump off any standing water and sweep away leaves first, so that dirty water does not slide into the pool. Take the cover off, clean it with a soft brush and a hose, let it dry completely and fold it for storage. A cover stored wet will grow mildew.
Step 2: Bring the water level back up
Top the pool up with a hose until the water reaches the middle of the skimmer opening. Remember that fill water changes your chemistry: if you add a lot of it, you will lower stabilizer and salt and may change calcium, alkalinity and pH. Test after filling, not before.
Step 3: Reconnect and start the equipment
- Remove the winter plugs from the skimmers and return lines, and the ice compensators.
- Put back the drain plugs on the pump, filter and heater, and reinstall the salt cell.
- Check O-rings and lubricate them with a silicone-based pool lubricant. Replace any that are cracked.
- Fill the pump basket with water to prime it, then turn the pump on and check for leaks and air in the lines.
- Check the filter pressure and note the clean reading: you will use it to know when to clean the filter.
- Only start the heater once water is flowing normally.
Step 4: Clean the pool
Net out the leaves and debris, brush the walls and floor and vacuum. Removing organic debris before shocking means your chlorine goes to work on bacteria and algae instead of on leaves.
Step 5: Test and balance
With the water circulating for a few hours, test everything. Adjust in this order, waiting a few hours between steps:
- Total alkalinity to 60–120 ppm (alkalinity calculator).
- pH to 7.2–7.6 (pH calculator).
- Calcium hardness to the range for your surface (calcium calculator).
- Stabilizer (CYA) to 30–50 ppm, or 60–80 ppm for a saltwater pool (CYA calculator). Stabilizer dissolves slowly, so add it early.
- Salt, if you have a salt system (salt calculator).
If your water level dropped a lot over the winter and you refilled with a lot of fresh water, expect stabilizer and salt to be noticeably lower than when you closed.
Step 6: Shock
Once pH is in range, raise free chlorine to shock level (about 40% of your CYA, at least 10 ppm) using the shock calculator. Shock at dusk, with the pump running. If the water is green or cloudy, follow our green pool guide and keep chlorine at shock level until the water clears, instead of adding a single dose.
Step 7: Filter until clear, then swim
Run the pump 24 hours a day for the first few days and clean or backwash the filter when the pressure rises 8–10 psi above its clean reading. Before swimming, check that:
- The water is clear and you can see the main drain.
- Free chlorine has dropped back to your normal range for your CYA (see the chlorine calculator).
- pH is between 7.2 and 7.8.
Opening checklist
- Clear and remove the cover.
- Top up the water.
- Remove the winter plugs, reinstall drain plugs and the salt cell.
- Prime and start the pump; check for leaks.
- Clean, brush and vacuum.
- Test and balance: alkalinity, pH, calcium, stabilizer, salt.
- Shock and filter around the clock until clear.
At the end of the season, our pool closing guide walks you through winterizing.
Safety first: Always read the product label. Add chemicals to water, never water to chemicals. Add one chemical at a time with the pump running, never mix products (especially chlorine and acid), and keep everyone out of the water until levels are back in range. Wear gloves and eye protection when handling acid or shock.
Sources and methodology
Last reviewed: November 2026. Doses are calculated from the chemistry of each product (molecular weights and available chlorine) and cross-checked against manufacturer and industry dosing charts. Recommended ranges follow CDC guidance for home pools and hot tubs.
Frequently asked questions
How long after opening a pool can you swim?
Usually 24–72 hours. Wait until the water is clear, free chlorine has dropped back to your normal range and pH is between 7.2 and 7.8.
Should I shock the pool when opening it?
Yes. After months without chlorine, a shock to about 40% of your stabilizer level (at least 10 ppm) kills anything that grew over the winter. Balance pH first so the chlorine works efficiently.
My pool is green after winter. What now?
Clean out debris, balance pH, then keep chlorine at shock level until the water clears, following our green pool guide. A single dose of shock is rarely enough.