woman with cocktail by pool.png
man swimming in pool.png
woman relaxing in pool.png


How a pool is closed/maintained for the off season will affect how easy the pool will be to open in the spring. The ultimate objectives in closing/maintaining a pool for the winter months are to preserve water quality, protect equipment and pool finishes, and have a pool ready for enjoyment with a minimum of effort.


This Technical Information Bulletin discusses the subject of off season operation as opposed to off season closing using BioGuard stabilised chlorinating sanitisers.


Winter Operation of Covered Pools

In mild climates where the water may not freeze for weeks at a time, many people may prefer not to close the pool. The benefits of not totally closing a pool include:

  • Easier and faster reopening with fewer problems (such as cloudy water or algae) to take care of during reopening.
  • Greatly reduced chemical usage and maintenance during the period of reduced operation.
  • Less chance of having surface damage or equipment problems.


The following guidelines detail the general procedure for off season operation of a pool; clean the pool, balance the water, circulate, shock, add an algaecide, cover the pool, and test the water periodically.


1. Clean the pool and solve any current problems (such as algae) before closing the pool. Dirt  leaves, and algae can cause staining if not removed before covering. Backwash the filter and clean it with Strip-Kwik Filter Cleaner and Degreaser to remove accumulated greases and oils in the filter. If you have hard water in your area or have used greater than normal amounts of calcium hypochlorite this year (perhaps to solve a chlorine demand), use Kleen-It® Filter Cleaner to dissolve scale and other accumulated debris which may be present in the filter.

2. Balance the water for lower temperatures. Lower temperatures make calcium more soluble and can create a potential staining, scaling or surface degradation problem, especially for plaster pools. The Saturation Index can be a useful tool for determining proper water balance. ALEX can help you determine how to balance your water for colder temperatures (use the "Winter" program). Adjust the pH to 7.7. Total alkalinity to 150 ppm. Maintain a minimum calcium hardness of 200 ppm in plaster (gunite) pools and 150 ppm in vinyl pools. At a temperature of 0°C, the SI would be -0.3.

3. Run pump and circulation at least 4 hours a day. For pools with feeders, add the proper BioGuard product to the feeder as necessary and adjust the flow rate down a bit to maintain minimum sanitiser concentrations (0.5-1.0 ppm free chlorine is sufficient). As the temperature drops through the winter, the feeder flow rate should be reduced. Then as temperatures begin to warm, slowly increase the flow rate. If a feeder is not used, a floater filled with BioGuard Stingy Sticks can be tied off and added to the pool to help sanitize the pool.

CAUTION: Since the pump is not being run for as long as normal, remove any BioGuard Stingy Sticks, or Tablets (or any sanitising product) from the skimmer. A 4-hour circulation time may allow acidic water (if using trichlor sticks or tabs) to accumulate in piping below the skimmer. This may cause pump and equipment concerns. Smart Sticks may remain in the skimmers as a source of sanitiser.

4. Shock the pool with Burn Out or Burn Out 35 before covering to help eliminate any oxidisable debris which may create water or surface discoloration or sanitation difficulties. Make sure these products are fully dissolved in the pool water by brushing the pool following this addition.

5. Back-Up algaecide should be added before covering the pool to help prevent algae growth. An initial dose added following label directions will work quite well. A maintenance dose would be beneficial every three months to reduce the potential for staining.

6. Cover the pool to prevent the accumulation of dirt and debris. A solid cover will work the best to keep dirt out of the pool. If a mesh cover is used, see the section on "uncovered" pools at the end of this bulletin for additional guidelines.

7. Adjust the frequency of water testing according to the average water temperature and adjust the feeder mechanisms as necessary to maintain 0.5-1.0 ppm free chlorine.


Check pH and total alkalinity monthly.


Inspect all equipment for proper operation, especially electrical controls on heaters and pumps. If freezing conditions are anticipated, periodic inspections during the winter are advised.


CAUTION: If periodic freezing temperatures occur, the heater may need to be run several hours a day to keep

water temperatures above freezing. When the air temperature falls below 0°C, circulate the entire system continuously to keep ice formation to a minimum.


Uncovered Pools

For pools which will not freeze and WILL NOT BE COVERED, the above recommendations would still apply. However, it will be necessary to periodically vacuum and brush the pool to eliminate accumulated debris, dirt, and leaves. Regular cleaning and removal of dirt and debris will help prevent surface staining and allow added sanitisers to work more effectively.


The above information is supplied by Bio-Lab and represents its best interpretation of available technical information at the time of preparation. The sole purpose is to supply factual information to Bio-Lab customers. It is not to be taken out of context nor used as support for any other claim not made herein.