How to Close a Pool (Winterize)
A step-by-step guide to winterizing your pool: balance the water, lower the level, blow out the lines, add antifreeze and winter chemicals, and put the cover on right.
Closing a pool the right way protects your plumbing from freeze damage and means a clean, easy opening next spring. The sequence is: balance the water a few days ahead, lower the level below the skimmer, blow out and plug the lines, add pool antifreeze where needed, dose your winterizing chemicals, then cover the pool tight. Do these in order and you avoid cracked pipes and a green pool come April. Here is the full process.
Pool Closing and Winterizing Gear
In The Swim Pool Closing Kit (Winterizing Chemicals)
Bundled winter shock, algaecide, and oil absorber sized to your pool.
Robelle Heavy Duty Winter Pool Cover
Durable above-ground winter cover that blocks light, leaves, and rain.
CPDI Swimming Pool Antifreeze, 4 Gallon
Non-toxic propylene glycol antifreeze to protect plumbing lines from freezing.
Doheny's Ultimate Pool Closing Kit
Complete winterizing chemical set for above-ground and inground pools.
Step 1: Balance the water first
Start three to five days before closing day. Water that sits all winter slightly out of balance can stain, scale, or corrode surfaces over months, so dial it in now.
- pH: 7.2 to 7.8, ideally near 7.4 to 7.6.
- Total alkalinity: 60 to 120 ppm to buffer pH all winter.
- Calcium hardness: 200 to 400 ppm to protect plaster and equipment.
- Free chlorine: a normal level for your CYA going into the cold.
Set pH and alkalinity carefully with our pH and alkalinity calculator, and work the full sequence with our pool water balance guide. Slightly higher pH and alkalinity, near the top of range, gives you a buffer against the gradual drift that happens under a closed cover.
Step 2: Deep clean before you cover
A clean pool overwinters far better than a dirty one. Skim the surface, brush the walls and floor, and vacuum up any debris. Empty the skimmer and pump baskets. The less organic material left in the water, the less there is for algae to feed on once chlorine fades, so this cleanup directly affects how your spring opening goes.
Step 3: Lower the water level
Drop the level so water is not sitting in the skimmer and return lines where it could freeze.
- For a mesh safety cover or a hard-freeze climate, lower 4 to 6 inches below the skimmer and returns.
- For a solid floating cover, lowering just below the skimmer is often enough.
- Use the filter on the waste setting or a submersible pump. Never fully drain an inground pool, since groundwater can float or lift the shell.
Step 4: Blow out and plug the lines
This is the step that prevents cracked pipes, so do not skip it in any freezing climate.
- Use a shop vac or a dedicated blower to push air through each line until it bubbles freely out the return or skimmer.
- Plug each return with a threaded winterizing plug while air is still flowing, so the line stays empty.
- Use a skimmer plug or a freeze-protection device such as a Gizzmo in the skimmer.
- Pour pool antifreeze into the lines where the label directs as backup protection. Never use automotive antifreeze, and do not pour antifreeze into the pool body.
Step 5: Drain and store the equipment
Pull the drain plugs from the pump, filter, heater, and chlorinator so no water is left inside to freeze. For a sand or DE filter, set the multiport valve to winterize. Store the pump indoors if you can, along with the plugs and any removable gauges. Bag and label your plugs so spring opening is painless.
Step 6: Add winterizing chemicals
With the pump still running, add your winter chemicals so they mix fully before you close. A typical closing dose is a shock plus a long-acting winter algaecide, and many closing kits bundle these with an oil absorber.
Safety basics that always apply:
- Never mix pool chemicals. Add each product separately, and never combine shock with tablets or acid in a container.
- Always add chemical to water, not water to chemical. Pre-dissolve or broadcast granular products per the label.
- Run the pump while dosing, then let it circulate before you shut down.
- Do not let concentrated chlorine sit against a vinyl liner under the cover, since it can bleach it.
- Store leftover chemicals dry, separated, and away from kids and pets.
| Closing task | Why it matters | Target or note |
|---|---|---|
| Balance water | Prevents winter staining and scale | pH 7.4 to 7.6, TA 80 to 120 |
| Lower water level | Keeps lines from freezing | 4 to 6 in below skimmer in freeze zones |
| Blow out lines | Stops cracked pipes | Plug returns, plug skimmer |
| Add antifreeze | Backup freeze protection in lines | Pool-safe only, never in the pool body |
| Winter chemicals | Holds water clear until spring | Closing shock plus winter algaecide |
| Cover tight | Blocks light, leaves, debris | Secure with water bags or clips |
Step 7: Put the cover on
Install a clean, well-fitting winter cover and secure it so wind cannot lift it. Block sunlight to limit algae, and keep leaves and rain out. For a solid above-ground cover, use a cover seal or clips and an air pillow to keep water and ice off the center. For a safety cover, anchor the straps evenly. A cover pump on top through winter stops a heavy puddle from forming and stretching the cover.
That is it. A pool closed clean, balanced, freeze-protected, and tightly covered opens clear and easy next spring. When the weather warms, walk through our spring pool opening guide to reverse the process.
Pool Care & Maintenance Planner
Water-test log, chemical dosing tracker, weekly maintenance schedule, and opening and closing checklists, in one printable planner that keeps your pool clear all season.
Frequently Asked Questions
When should I close my pool for winter?
Close once water temperatures stay reliably below about 60 degrees, usually mid to late fall. Algae and bacteria grow slowly in cold water, so closing cold keeps the pool cleaner over winter. Closing too early while the water is still warm lets algae bloom under the cover, so wait for a steady cold snap rather than a calendar date.
How low should I drain the water before closing?
It depends on your cover and plumbing. For a mesh safety cover or in freezing climates, lower the water 4 to 6 inches below the skimmer and returns so water does not sit in the lines. For a solid floating cover you often lower it just below the skimmer. Never fully drain an inground pool, since it risks the shell lifting from groundwater.
Do I really need to blow out the lines?
In any climate that freezes, yes. Water left in pipes expands when it freezes and can crack plumbing, fittings, and the pump or filter. Blowing the lines clear with a shop vac or blower, then plugging them and adding pool antifreeze where needed, is the single most important step for preventing expensive freeze damage over winter.
Is pool antifreeze the same as car antifreeze?
No, and you must never use automotive antifreeze in a pool. Car antifreeze is toxic and not made for pool plumbing. Pool and spa antifreeze is a non-toxic propylene glycol product designed to protect pool lines. Even so, you blow the lines out first and use antifreeze only as backup protection in the plumbing, never poured into the pool itself.
Should I add chlorine right before I close?
Balance the water and bring chlorine to a normal level a few days before closing, then add winterizing chemicals on closing day. Many owners add a closing shock and a winter algaecide so the water stays protected. Avoid floating a chlorine product directly against a vinyl liner under the cover, since concentrated chlorine sitting in one spot can bleach or damage it.
Why is my pool green when I open it in spring?
A green spring opening usually means the water was not fully balanced at closing, chlorine ran out over winter, or the cover let in light, leaves, and rainwater. Closing late while the water was still warm makes it worse. Balancing carefully, shocking, and dosing a winter algaecide at closing, plus a tight cover, is the best prevention.
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