To close a pool, you typically need a combination of balancing chemicals, shock treatment, algaecide, and other winterizing treatments. However, not every pool needs every closing chemical, and adding products you don’t need can throw off the water balance or create more work when you reopen in the spring.
The key is to test the water first and only add what your pool actually needs.
In this post, we’ll break down the main types of chemicals you may need to close a pool, what each one does, and which winterizing treatments are actually necessary.
The exact chemicals you need will depend on your test results, your pool setup, and how you plan to winterize it. Some are used to balance and sanitize the water, while others help prevent algae, staining, scale, or freeze damage over the winter.
Here are the main types of chemicals you may need when closing a pool.
Water-balancing chemicals help bring your pool’s pH, total alkalinity, and calcium hardness into the proper range before closing. Keeping those levels balanced helps protect pool surfaces and equipment and reduces the risk of corrosion, staining, or scale while the pool is closed.
Which water-balancing chemicals you need before closing depends on which level is out of range:
If these levels are already within the recommended range, you can typically skip this step.
Pool shock delivers a strong dose of sanitizer to the water before the pool is closed. It helps break down sweat, oils, leaves, and other organic material that can consume chlorine and contribute to algae, cloudy water, staining, and odors over the winter.
For most pools, shocking is a standard part of closing, especially if the water has seen heavy use or the chlorine level is low. Just be sure to use a shock that’s compatible with your pool, and add the correct amount for your pool size. This helps leave the water properly sanitized going into winter and can make spring opening easier.
Algaecide helps prevent algae from taking hold while the pool is covered and circulation is reduced or shut down. It can be especially useful if the pool tends to develop algae, the water will sit closed for several months, or you’re closing while temperatures are still relatively warm.
For winter closing, look for an algaecide labeled for long-term or winter use. Some standard algaecides are designed for short-term treatment, while winter formulas are intended to protect pools for a longer stretch of time.
Since metals such as iron or copper and high calcium levels can leave stains or scale on pool surfaces while the water sits over winter, it can help to add a stain and scale preventer before closing a pool. It helps keep those minerals suspended in the water rather than letting them settle onto the pool surface.
This treatment is most useful for pools with a history of staining, metal-related discoloration, or high calcium hardness. So, if you haven’t been experiencing these types of pool problems, you may not need to add one just for closing.
Pool antifreeze is a little different from the other chemicals on this list because it goes into the plumbing, not the pool water. It’s mainly used in colder climates like Ontario if there’s a chance some water could remain in the lines and freeze over winter.
Of course, if the lines are fully blown out and sealed, you may not need antifreeze at all. But if you do, choose a non-toxic product made for pools or plumbing systems.
Something like automotive antifreeze, though often the more convenient option, doesn’t belong anywhere in a pool system.
No, you don’t necessarily need winterizing chemicals when closing a pool. Once you’ve balanced, sanitized, and treated the water for any known issues, extra winter products are usually just there to solve a specific problem or make the off-season easier.
Here are some optional winterizing chemicals and the specific problems they’re designed to help with:
If your pool usually opens clean and clear in the spring, you may not need any of these extras. They make the most sense when they address a problem your pool actually has.
Every pool closes a little differently, and knowing which treatments are actually worth using can be part of the challenge. If you’d rather leave those decisions — and perhaps the rest of the closing process — to someone else, Clark Pools & Spas offers professional pool-closing service in Collingwood and the surrounding area.
Our team can help get your pool ready for winter before freezing temperatures arrive, so you’re not piecing the process together on your own. Book your pool closing today.
