For pools that are winterized, or closed during winter, the water is essentially stagnant for 7 months, without circulation and filtration.

The proper type and amount of pool closing chemicals used during pool close-down will determine the condition of the water come spring start-up, and along with good water balance, will protect your soft and shiny pool surfaces from staining or corrosion.

Use the wrong winter pool chemicals, or not enough of the right chemicals, and you could end up paying for it come springtime, in terms of algae, stains and days or weeks of lost summertime, waiting for the water to clear.

Before adding any of your pool closing chemicals, it’s important to test and adjust all water balance parameters, so that your closing chemicals work at their best, to prevent staining and scaling during winter. Put away your closing kit for now, and pull out your test kit – to verify that your pool chemical levels are within these ranges:

To raise Calcium Hardness: Add Calcium Increaser to raise water hardness levels, and when too high, dilute with softer, fresh water. 3/4 lb. of Calcium Up will increase hardness by 10 ppm in 10,000 gallons of water.

To adjust Alkalinity: Add Alkalinity Increaser to raise total alkalinity levels and when too high, use pH Reducer. 1 lb. of Alkalinity Up will increase alkalinity by 10 ppm in 10,000 gallons of water, and 1 lb. of pH Down will reduce alkalinity by 10 ppm in 10,000 gallons of water.

To adjust pH: Add pH Increaser to raise pH levels and when too high, use pH reducer. 1/4 lb. of pH Down will decrease pH by 1 decimal point, in 10,000 gallons of water, and 1/4 lb. of pH Up will increase pH by 1 decimal point, in 10,000 gallons of water.

After balancing the water, shock the pool, following package label instructions to oxidize contaminants and disinfect the pool water. Be sure the pool is clean of leaves and debris, which consumes shock and algaecide. Your pool water should also be clear and free of algae when closing the pool for winter.

There is no product known as ‘winter pool shock’, you can use chlorine shock or non-chlorine shock. If you use chlorine shock however, you must wait before adding stain & scale or winter algaecide. High chlorine levels will destroy other winter chemicals.

To repeat - chlorine pool shock can breakdown your winter stain and algaecide chemicals, rendering them useless. Chlorine shock can also damage floating pool covers, when installed immediately after shocking. If you use chlorine shock to close the pool, shock the pool 2-5 days before closing, or add stain and algaecide winter chemicals a few weeks later, under the cover.

This is why our Winter Kits contain non-chlorine shock, although best practice is to add the non-chlorine shock the evening before you plan to close the pool.

There are 3 main types of pool algaecides, Quats, Polymers, and Copper based algaecide. All 3 types can be used effectively as a winter algaecides. Remember that high chlorine levels can disrupt or destroy pool algaecides, test the water to be sure chlorine level is below 4 ppm, before adding winter pool algaecides.

In The Swim Winter Algaecide is a chelated (non-staining) form of elemental copper that acts as a powerful herbicide and fungicide.

In The Swim Algaecide 60 Plus is a 60% polymer algaecide, known as POD, in a non-foaming and non-staining formula that is long lasting and powerful.

IntheSwim Algaecide 50 is a 50% quat algaecide, known as DDAC with broad-spectrum ability to kill all algae types in pools.

For pools with mesh winter covers, or loose covers that allow leaves to enter the pool, a double dose of algaecide is recommended. For best results add a second treatment, under the cover, in early spring or as temperatures begin to warm.

For pools with mesh covers, or solid covers in poor condition, use enzymes during winter to consume organics and oils, reducing the work of your algaecide and preventing waterline stains around the pool. Enzymes are especially popular in areas of urban air pollution, rural farm dust, or heavy spring tree pollen. Not needed if your pool opens up blue and clear every year, but if not…

Natural Chemistry’s Pool Magic Spring & Fall is an excellent enzyme treatment for pools that need extra help during winter, to prevent major spring clean-ups.

Natural Chemistry’s Pool Magic Spring & Fall + PhosFree is the same great formula, but with the addition of PhosFree, to remove phosphates in the pool water.

AquaPill’s WinterPill is a concentrated floating ball of enzymes that is punctured with a small hole, to slowly release 16 ounces of powerful enzymes all winter long.

In addition to a winter algaecide, a slow-release floater to distribute sanitizer all winter long is a good idea, especially for mesh covers, or loose fitting solid covers, or any winter cover with small holes.

You can fill up a large chlorine floater with chlorine tablets, and tie it off in the middle of the pool, so it does not tip over, or come to rest against the wall or on a step, which could stain or damage pool plaster and vinyl liners.

This is why our Winter Kits include a non-chlorine winter floater, filled with a chlorine free sanitizer that is safe for all pool surfaces. Our special blend of oxidizer also removes carbon dioxide from the water, a nutrient vital for algae growth.

We don’t sell our non-chlorine winter pool floater separately, but it is part of our pool closing kits.

Antifreeze: Not a water treatment chemical, use non-toxic pool antifreeze in underground plumbing pipes to prevent freezing during winter.

Filter Cleaner: Use our pool filter cleaner chemicals to remove scale and oils from your filter. The best time to clean your pool filter sand, cartridge or grids is during closing, before it sits dry all winter.

Stain & Scale: Included in our pool closing kits is a bottle of Stain Away, a powerful sequestering agent to prevent metal stains and mineral scale from forming during cold winter temperatures.