Pool opening checklist
Open the pool in this order: remove the cover, reinstall equipment, top up the water, run the pump, and then test and dose.
Always follow your product’s label directions. Pool and spa chlorine, bromine, shock and algaecides are EPA-registered pesticides: use products labeled for pool or spa use, and don’t swim or soak until levels are within the limit on your product’s label. If this page and a label disagree, the label wins.
On this page (8 sections)
Clear the cover before you remove it, and run the pump for several hours before you test. Dose chlorine first, then alkalinity and pH. For a 20,000-gallon pool opening at 0 ppm free chlorine with 30 ppm stabilizer, the first chlorine dose is about 82 fl oz of 12.5% liquid chlorine.
Before you start: supplies
Hayward's opening guide starts with a simple check that saves a second trip: make sure your test kit and chemicals have not expired. Leftover liquid chlorine from last season has lost much of its strength, especially if it sat in a hot garage, so plan to buy fresh jugs. Have these ready:
- A test kit that reads free chlorine (FC), pH, total alkalinity (TA), calcium hardness (CH), and stabilizer (CYA) and is not past its date.
- Liquid chlorine (10% or 12.5%), muriatic acid, and baking soda. Stabilizer and calcium chloride only if last fall's numbers or this spring's test call for them.
- A cover pump or submersible pump, a leaf net, a soft broom, a hose, and a place to dry and fold the cover.
- Replacement O-rings and lubricant for the pump lid, and the drain plugs you stored in the fall.
- Gloves and eye protection for chemicals.
Step by step
- Clear the cover. Pump off standing water and remove leaves before you pull it, so the debris doesn't slide into the pool.
- Remove the cover slowly, folding it in halves. Clean it, let it dry fully, and store it off the ground.
- Remove winter plugs from skimmers and return lines, and take out any ice compensator or skimmer protector.
- Reinstall equipment: drain plugs in the pump, filter, and heater; skimmer baskets; return fittings; ladders and rails. Check O-rings and lubricate the pump lid seal.
- Top up the water to the middle of the skimmer opening.
- Start the system. Turn the power on, prime the pump, and check the equipment pad for leaks. Note the filter pressure. Backwash or clean the filter if it is already high.
- Circulate for several hours before testing, as Hayward recommends, so the test reflects the whole pool, not the water near the returns.
- Test and dose in order: chlorine first if low, then alkalinity, pH, calcium, and stabilizer. Use the calculator below.
- Brush and vacuum the next day, once the first chlorine dose has worked overnight. Check filter pressure again: opening debris clogs filters fast.
- Retest free chlorine and pH that evening and every day for the first two weeks.
First test and start-up doses
Enter your first test. The calculator gives start-up doses in the order to add them, for the products you have. Opening is the time of year when your numbers are most likely to be far off, so expect several steps.
Here is a typical example from our engine: a 20,000-gallon plaster pool opens at free chlorine 0, pH 7.9, TA 110 ppm, CH 250 ppm, and CYA 30 ppm, with water at 62 °F. The plan is two steps:
| Step | Amount | Change |
|---|---|---|
| 1. Liquid chlorine 12.5% | 82 fl oz | FC 0 → 4 ppm (minimum for CYA 30 is 2.5 ppm) |
| 2. Muriatic acid 31.45%, 30 minutes later | 24 fl oz | pH 7.9 → 7.5 |
Computed with the same engine as our calculators. TA, CH, and CYA were already in range, so the plan skips them. Retest FC and pH 30 minutes after the acid.
Stabilizer is the number that surprises people in spring. If you drained part of the pool over winter, or rain overflowed it, CYA is lower than last fall. If you refilled completely, it is zero. Stabilizer needed to bring fresh water up to a starting level:
| Pool size | To 30 ppm | To 40 ppm |
|---|---|---|
| 10,000 gal | 2.5 lb | 3.35 lb |
| 15,000 gal | 3.75 lb | 5.0 lb |
| 20,000 gal | 5.0 lb | 6.7 lb |
| 25,000 gal | 6.25 lb | 8.35 lb |
| 30,000 gal | 7.5 lb | 10.0 lb |
Computed with our engine. Liquid stabilizer is weaker per pound: use the percent on its label in the pool stabilizer calculator. Add it through the skimmer or in a sock in front of a return, don't backwash for a few days, and retest in 3–7 days. Salt pools usually target 60–80 ppm.
Always follow the product label. It is a violation of federal law to use a pesticide product in a manner inconsistent with its labeling.
Never mix chlorine and acid, or two chlorine products. Add each one separately with the pump running, 30 minutes apart. Add chemicals to water, never water to chemicals. Wear gloves and eye protection. No one should swim until FC is back in your target range and at or below the swim limit on the product label (often 4 ppm), and until at least 30 minutes have passed since the acid. Poison Control: 1-800-222-1222.
Green or cloudy at opening
A green or murky pool under the cover is common after a warm spring. The fix is the same as any other time: shock with a product labeled for shocking pools, using the amount on its label and waiting as long as the label says before anyone swims.
- Green or you can't see the floor: follow the green pool guide. Shock labels usually give an amount per 10,000 gallons, so the 20,000-gallon example pool above takes twice that amount. Keep people out until FC is at or below the label's swim limit, often 4 ppm. If the water hasn't cleared after a few days of following the label, call a pool professional.
- Cloudy but not green: check the filter first (pressure, clean media), then chlorine. See cloudy pool water.
- Clear but chlorine won't hold: something is still consuming it, often algae you can't see yet. Shock it by the label the same way, then run the overnight chlorine loss test: a drop of 1 ppm or less means chlorine is holding.
Don't try to fix pH and alkalinity precisely during a shock: very high chlorine makes the pH test unreliable. Keep pH roughly in range, clear the water, and then balance.
First two weeks
- Test FC and pH every day and top up chlorine in the evening. Write down how much you add: after a week you will know your daily loss, which sets your maintenance schedule.
- Watch filter pressure. Spring pollen and debris clog the filter quickly. Clean it when the pressure rises as far as your filter's manual says.
- Brush every few days, especially steps, corners, and behind ladders.
- Retest stabilizer and calcium after about a week, once anything you added has dissolved. Your chlorine target follows CYA.
- Keep last fall's numbers handy. If you saved your closing readings, compare: a big drop in CYA or CH tells you roughly how much water you lost over winter.
Printable checklist
- ☐ Test kit and chemicals within date; fresh liquid chlorine
- ☐ Cover pumped, cleaned off, removed, dried, and stored
- ☐ Winter plugs and ice compensators out
- ☐ Drain plugs, baskets, return fittings, and ladders back in; pump lid O-ring lubricated
- ☐ Water topped up to mid-skimmer
- ☐ Power on, pump primed, no leaks, filter pressure noted
- ☐ Pump run for several hours before the first test
- ☐ First test entered; chlorine, then TA, pH, CH, and CYA dosed with 30-minute gaps
- ☐ Next day: brush, vacuum, check filter pressure, retest
- ☐ Daily FC and pH for two weeks; CYA and CH retest after a week
Closing again in the fall? The inground closing guide covers what to record so next spring is easier.
FAQ
What chemicals should you put in your pool when you first open it?
After the pump has run for several hours, test the water. Add chlorine to reach your target (if the water is green, shock it as the product label directs instead). Then add baking soda or acid to bring alkalinity and pH into range. Add calcium and stabilizer only if the test shows they are low, for example after draining or heavy rain over winter.
Should I add algaecide or pool shock first when opening my pool?
Shock (chlorine) first. Chlorine does the actual work of killing algae. Algaecide is optional. If you use one, add it after chlorine has come back down to the range its label names, and never mix the two in a bucket.
How long should I run my pool pump when I open it?
Run it for several hours before your first test, as Hayward's opening guide recommends. After that, we suggest running it around the clock until the water is clear and chlorine holds overnight, then switching to your normal schedule. The pump run time calculator gives normal hours for your pump and pool.
Sources
- Hayward, The ultimate guide to opening your pool: hayward.com
- Hayward, Opening your pool: hayward.com
- PHTA fact sheet, Sodium hypochlorite (strength loss in storage): phta.org
- CDC, Model Aquatic Health Code 2024, Annex (chlorine and CYA): cdc.gov (PDF)
- CDC MMWR, Pool chemical injuries, 2008–2017: cdc.gov