There is a special non-toxic anti-freeze made specifically for swimming pools. It is made especially for the protection of your plumbing lines for your swimming pool and helps protect the lines from freezing. Usually swimming pool owners in the northern states that have freezing temperatures will want to do this to help avoid costly repairs.
Swimming pool anti-freeze is non toxic so it is safe for swimmers and there should be no interference with your routine chemical maintenance. When opening your pool for the spring, you should drain the anti-freeze from your pool equipment before use.
If you decide not to use anti-freeze in your plumbing lines and fittings, make sure that you remove all water by using a shop vac to blow all the water out of your lines. We recommend that you then plug your skimmers and return lines, to keep any water from getting back in.
Also make sure you completely winterize your heater also. If water remains in the lines or pool equipment, and your area experiences a hard freeze, your plumbing lines, filter, or other equipment can have cracks where the ice expanded when spring time comes.