You really only need one chemical (algaecide) to properly winterize a swimming pool. You need some other stuff to protect your pool from harsh winter conditions, but only one chemical to add when closing.
The answer is — it's not necessary if you properly blew out the lines. That task gets water out of the pipes so they don't freeze during winter. But if you properly winterized your pool, there should be no need to add antifreeze.
When closing and winterizing your pool, it is important to remember to balance your pool water's chemistry prior to closing and don't forget the algaecide.
Green discoloration in a swimming pool is caused by the growth of algae, a type of green aquatic plant that floats on the surface of water. Algae usually flourishes in warm water but can still take over your pool in winter if given half a chance.
We recommend an optional winter cover for inground pools because it makes winter maintenance easier. ... Never use chlorine tablets during the winter: you'll want to opt for Assault 73 Shock or Quick Shock granular chlorine once a month (1 pound per 10,000 gallons.)
Clear pipes and equipment of water using a blower or compressor and plug the pipes at the pool. Add swimming pool antifreeze to the lines to prevent freezing. Place a Gizzmo* (or similar device) in the skimmer to seal it and absorb pressure from ice.
Swimming pool antifreeze, also called non-toxic antifreeze, is the same stuff that RV owners can use in their motor home water systems. For swimming pool use, it can protect swimming pool pipes down to -40°, when added in correct proportion. Here's some Q&A regarding the use of pool plumbing antifreeze.
Shocking the pool during the winter months can certainly help to avoid a green swamp-like pool in the spring. It's often recommended. However, poor water balance or improper application can lead to unintended consequences, such as discoloration and damage to pool surfaces.
Several days before closing, shock the pool with a chlorine shock or non-chlorine shock, using at least 2 lbs per 10,000 gallons (follow package directions). Allow the chlorine level to return to 1.0-3.0 ppm before adding any winter algaecide or your pool cover.
Shocking kills any bacteria that might linger in your pool during the winter. We recommend shocking a few days before you close the pool. If that is not possible, make sure to shock the pool the night before you close it for winter.
Helpful tips to keep your pool and its equipment safe during freezing temperatures. Run your pool pump continuously when temperatures are near or below freezing. You don't need to run your heater, moving water likely will not freeze.
Keeping your pool warm is the most effective way to avoid freeze damage, period. As long as you can keep your pool water moving, and at a constant temperature above the freezing point of 32 degrees, you're safe.
Insulate plumbing lines with blankets or towels to prevent freezing. Even pool noodles can serve as good insulation around pipes. Open all lines to ensure proper water flow. If a valve is shut off, no water will flow through that pipe, and there is the danger of freezing damage.
Using our skimmer cover, the Skimmer Plug for aboveground pools (shown here) will keep a thick ice sheet from freezing into the inside of the skimmer, which can crumple the wall below the skimmer, if the ice sheet shifts or if the pool loses even a small amount of water supporting the ice sheet.
Use salt test strips for an accurate reading and when the season starts cooling down, do not add anymore salt to the pool. It is better not to have a lot of salt in your pool toward the end of the season. Balancing your water's chemistry is important for all pools during closing time.
Short answer: yes. Longer answer: it depends on the formulation. The label on every bleach bottle should tell you the ratio of sodium hypochlorite (and available chlorine) in the bottle to everything else. A higher percentage is generally better, as you'll need to use less bleach to treat your pool.
So while a solar cover won't actually 'turn your pool green', it will warm your water by up to 8 degrees, so if the other conditions are right, adding a solar cover can easily accelerate algae growth, very rapidly. You need to get the water balance in your pool right before putting the cover back on.
A late September or October closing is a great way to set up for success in the spring. If you are already suffering from an algae bloom; take care of that before you close. Opening your pool early in the spring is a good idea if you want clear water.
Most experts recommend waiting at least until temperature drops below 65 degrees Fahrenheit (18 degrees Celsius) to winterize your pool. However, if you can wait longer until your pool is below 50 degrees Fahrenheit (10 degrees Celsius), you will have a much lower risk of problems occurring.