Do I Need to Clean My Pool Before Closing? Winter Prep Guide

Tools & Supplies Needed

Find on Amazon: Pool Closing Chemical Kit , Pool Test Kit , Pool Brush , Liquid Chlorine

Quick Answer

Yes, you absolutely must clean your pool thoroughly before closing it for winter. Failing to clean properly will lead to algae blooms, staining, equipment damage, and a nightmare reopening in spring. A clean pool going into winter means crystal clear water when you reopen.

Step-by-Step Pool Cleaning Before Closing

1. Remove All Debris
   Start by skimming the surface and vacuuming the bottom thoroughly. Remove every leaf, twig, and piece of debris. Even small amounts of organic matter will decay over winter, consuming chlorine and feeding algae growth. Pay special attention to corners, steps, and around pool fixtures where debris tends to accumulate.
2. Brush All Pool Surfaces
   Brush walls, steps, and floor systematically using a pool brush appropriate for your surface type. For plaster pools, use a stiff-bristled brush. For vinyl or fiberglass, use a softer brush to avoid damage. This removes biofilm and algae spores that aren't visible but will multiply rapidly in stagnant winter water.
3. Clean the Waterline
   Scrub the waterline with a waterline cleaner or mild abrasive to remove oils, scum, and mineral deposits. This prevents permanent staining during the months when water level remains constant. Use a pumice stone for stubborn calcium deposits on plaster surfaces, but never on vinyl or fiberglass.
4. Vacuum to Waste
   After brushing, vacuum the entire pool to waste (not through the filter). This removes the stirred-up debris and algae without clogging your filter system. If you don't have a waste setting, vacuum normally but be prepared to clean or replace your filter media immediately afterward.
5. Clean Pool Equipment
   Remove and clean all removable equipment including ladders, diving boards, skimmer baskets, and pool toys. Store these items in a dry location. Clean skimmer baskets thoroughly and reinstall them to catch any debris that might blow in during winter.
6. Service Your Filter System
   Clean or replace your filter media. For sand filters, perform a thorough backwash. For cartridge filters, remove and either clean thoroughly or replace with new cartridges. For DE filters, break down the grids and clean them completely. A clean filter ensures your closing chemicals can work effectively.
7. Balance Water Chemistry
   Test and balance your water chemistry before adding winterizing chemicals. Target pH between 7.4-7.6, total alkalinity 80-120 ppm (60-80 for salt water pools), and calcium hardness 250-350 ppm for plaster pools (lower for vinyl/fiberglass). Proper balance prevents equipment corrosion and surface damage during winter months.
8. Shock the Pool
   Add liquid chlorine to achieve shock level based on your CYA (stabilizer) level. Use the FC/CYA chart to determine proper shock level - typically 10-12 ppm free chlorine for pools with 30-50 ppm CYA. This kills any remaining bacteria and algae spores. Don't use calcium hypochlorite shock if you have high calcium levels, as this adds more calcium to your water.
9. Add Winterizing Chemicals
   After shocking, add your winterizing chemical kit according to manufacturer directions. These typically include algaecide, stain preventer, and enzyme products. Add these at least 24-48 hours before covering the pool to allow proper circulation and mixing.
10. Run Filtration System
    After adding all chemicals, run your filtration system continuously for 24-48 hours to ensure complete mixing and circulation. This distributes the winterizing chemicals throughout the entire pool volume and ensures nothing settles in dead spots.

Why Cleaning Before Closing Is Critical

Preventing Algae Growth: Any organic matter left in your pool becomes food for algae during winter. Even with winterizing chemicals, a dirty pool often turns green by spring, requiring expensive SLAM (Shock Level And Maintain) treatment to clear.

Equipment Protection: Debris can clog lines, damage pump impellers, and cause expensive equipment failures. Clean water protects your investment in pool equipment throughout the winter months.

Surface Protection: Leaves and debris can stain pool surfaces permanently if left to decompose over winter. Organic stains are often impossible to remove and may require acid washing or surface refinishing.

Easier Spring Opening: A properly cleaned and closed pool opens crystal clear in spring, saving you time, money, and frustration. You'll be swimming weeks sooner than neighbors who skipped proper closing procedures.

Common Cleaning Mistakes to Avoid

• Rushing the process - allow 2-3 days for proper cleaning and chemical balancing
• Skipping the brush step - this is critical for removing biofilm and algae spores
• Adding winterizing chemicals to unbalanced water - balance first, then winterize
• Covering the pool immediately after adding chemicals - allow circulation time first
• Using old or expired winterizing chemicals - these lose effectiveness over time

Safety Warning: Always add chemicals with the pump running and never mix different chemical products. Add chemicals in the evening to prevent sun degradation, and keep people and pets away from the pool area during chemical addition.