If you closed your above ground pool properly in the fall, you balanced the pH, alkalinity and calcium hardness, and perhaps shocked the water and added an algaecide. You drained and winterized the circulation system, plugged the water ports, removed the skimmer basket and covered the skimmer. You might have left the pool partially full of water and put an air pillow on the surface to prevent the cover from caving in under the weight of snow and ice. When you open the pool in the spring, you basically reverse the steps you took to winterize it. Even though the water was treated with chemicals in the fall, you should treat it again, and you'll probably have to manually clean the sides and bottom before you turn on the pump.
Clean the Cover, Remove and Store It
After months of winter weather, the pool cover will probably be laden with leaves and dirt. You don't want any of this debris to get into the water. First, drain any standing water off the cover; then clean the cover thoroughly with soap and water, and let it dry out before you remove it. Drying it out makes it easier to fold for storage, which you should do immediately to ensure it's in good shape for next winter.
Pool Opening Procedure
Now that you've uncovered the pool and removed the air pillow, the rest of the procedure for getting it ready to use is straightforward. If your pool has a removable deck, replacing it is part of the job. You may need help to do this.
Remove all the plugs from the water ports and the cover plate from the skimmer. If you installed an ice compensator in the skimmer, remove it before you replace the skimmer basket.
Add water to the pool. Before you turn on the circulation pump, the level should be at least to the halfway point on the skimmer basket.
Re-install the decking if you removed it in the fall. You'll need it to access the pool so you can do a manual cleaning and add chemicals.
Set up the pool pump, filter and other equipment. Reconnect any hoses you disconnected when closing the pool; put the drain plug back in the pump and set the multiport valve -- if you have one -- to Filter.
Turn on the pump, and check for leaks. If water doesn't circulate, you may need to prime the pump by removing the cover and pouring water in using a hose or a 5-gallon bucket.
Backwash the filter if you have a sand or DE filter. Attach a hose to the filter port; set the multiport valve to Backwash, and turn on the filter system. Water will flow out from the filter outflow port. Wait for the water to run clear before turning off the water -- this may take a couple of minutes. After backwashing, be sure to set the multiport valve back to Filter.
Brush down the sides and bottom of the pool to remove dirt that has collected over the winter. Some of this will float on the surface of the water, so remove it with a skimmer.
Treat the Water
Now that the pool is full and the circulation and filtration systems are working, it's time to balance the chemicals. You might want to take a sample of the water to a pool dealer to get it tested, but you can also do this yourself with a quality testing kit. After balancing pH, alkalinity and calcium hardness, it's a good idea to double-shock the water with 2 pounds of shock for every 10,000 gallons of water (or 5 gallons of liquid shock for every 20,000 gallons).
Turn on the pump, and let the water circulate for about 24 hours. Then vacuum out any debris that falls to the bottom of the pool. When the chlorine level falls below 5 ppm, the pool is ready for use.