When to Open
Open when daytime air temperatures consistently stay above 70°F (21°C). In most of the US, that's late April to mid-May. Opening too late is a bigger risk than opening too early — a covered pool sitting in warm weather with no circulation is a perfect algae incubator.
Rule of thumb
If you wait until it's hot enough to swim, you're two weeks late. Open early, get the chemistry right, and the pool will be ready when the first warm weekend hits.
What You'll Need
Full test kit
FC, pH, TA, CH, CYA. You'll need all five at opening — not just the quick FC/pH check.
Liquid chlorine (bleach)
You'll likely need a large opening shock dose. Buy at least 2–3 gallons of 10–12.5% liquid chlorine for a typical pool.
pH adjusters
Muriatic acid (to lower pH/TA) and baking soda or borax (to raise pH/TA if needed).
Brush, net, vacuum
The pool will have debris from winter. A leaf net, wall brush, and vacuum head (or robotic cleaner) are essential.
Teflon tape & lubricant
For reattaching drain plugs and lubricating O-rings. Use only Teflon-based or silicone lube — never petroleum-based, which destroys rubber gaskets.
Step-by-Step Pool Opening
Clean off and remove the cover
Pump or sweep standing water and debris off the cover before removing it — otherwise it all goes into the pool. If you have a mesh safety cover, skim any fine debris that settled through. Solid covers collect a lot of water; use a cover pump.
Clean and store the cover
Lay the cover flat on the deck or lawn, scrub both sides with a mild cleaner (no bleach — it degrades the material), rinse, and let it dry completely before folding. Store in a dry, shaded location. A wet, folded cover grows mold.
Reinstall drain plugs and fittings
Reinstall all drain plugs you removed when closing — pump, filter, heater, chlorinator, and any other equipment. Wrap threads with Teflon tape. Reinstall return eyeball fittings and skimmer baskets. Check that the multiport valve (if sand or DE filter) is in the "filter" position.
Fill the pool to mid-skimmer
The water level will have dropped over winter from evaporation and the lowering done at closing. Fill to the middle of the skimmer opening with a garden hose. If you're adding a lot of fresh water, CYA and salt levels will drop — you'll adjust in the chemistry step.
Prime and start the pump
Open the pump lid, fill the housing with water from a hose, close the lid, and turn on the pump. Open all suction and return valves. Watch for a steady flow through the return jets and a dropping pump strainer air bubble. If the pump won't prime after 2–3 minutes, check for air leaks at the lid O-ring or a closed valve.
Warning
Never run the pump dry. Even 30 seconds without water can damage the mechanical seal, causing a leak that's expensive to fix. Always prime first.
Skim, brush, and vacuum
Skim the surface, brush the walls and floor, and vacuum the bottom. For heavy debris, vacuum to waste to avoid clogging the filter on day one. This step matters — organic debris on the bottom will eat chlorine and cloud the water.
Test everything
Run the pump for at least 1 hour to circulate, then test all five parameters: FC, pH, TA, CH, and CYA. Write the results down — you'll need them all for the adjustment step.
Balance chemistry (TFP order)
Adjust in this order: TA → pH → CH → CYA → chlorine. This is the same TFP/PoolMath adjustment sequence used in regular maintenance — each step affects the ones after it, so the order matters.
Enter all five numbers into the Water Balance Calculator — it generates the full adjustment plan with exact chemical amounts.
Shock the pool
After balancing, hit the pool with a heavy shock dose — bring FC up to at least 10× your CYA level (the SLAM breakpoint). This kills anything that grew over winter. If the water is green or has visible algae, you're looking at a full SLAM process: hold shock level, brush twice daily, run the filter 24/7 until the water clears and FC holds overnight.
Use the Shock Calculator for the exact amount. See How to Shock a Pool for the full method.
Run the filter 24/7 for 24–48 hours
After shocking, run the pump and filter continuously for at least 24 hours. This circulates the shock dose, filters out dead algae and debris, and lets the chemistry stabilize. Check the filter pressure — you may need to backwash during this period if the water was dirty.
Retest and fine-tune
After 24–48 hours, test FC and pH again. If FC held overnight without dropping more than 1–2 ppm, the shock worked and the water is clean. Adjust pH if it drifted. Bring FC down to normal maintenance range (1–3 ppm for CYA 30) and resume your regular weekly maintenance schedule.
First-Swim Checklist
Don't swim until all of these are true:
FC is below 5 ppm (post-shock chlorine has dissipated to safe swimming level).
pH is between 7.2 and 7.6 (comfortable and effective).
Water is clear — you can see the main drain on the pool floor.
Pump, filter, and all equipment running normally with no leaks.
Safety equipment in place — fence gate latches, drain covers secured, rescue equipment accessible.
Common Opening Mistakes
Dumping the cover water into the pool
Standing water on the cover is full of tannins, algae, and debris. If it goes into the pool, you're starting the season with dirty water. Pump it off or sweep it off the side — never into the pool.
Skipping the full test
Only testing FC and pH at opening misses TA, CH, and CYA — all of which may have shifted over winter. You need all five to balance properly. Don't assume last year's numbers are still valid.
Opening too late
A covered pool with no circulation in 80°F weather breeds algae in days. By the time you open in June, you may be fighting a swamp instead of doing a routine startup. Open early — the chemicals cost less than an algae recovery.
Forgetting drain plugs
Turning on the pump with a missing drain plug on the pump, filter, or heater means water on the equipment pad and potential motor damage. Check every plug before startup.