Jordan Hidalgo Largo FL - What Chemicals Are Needed to Close a Pool?
Closing your pool properly at the end of the season is critical to protect your investment and make reopening easier in the spring. One of the most important steps is adding the right chemicals. These help prevent algae growth, maintain water balance, and protect your pool surfaces and equipment during the off-season.
Below is a breakdown of the essential chemicals you’ll need — and why each one matters.
🧪 1. Chlorine or Shock Treatment
Purpose:
Kills bacteria and algae before the pool is closed
Sanitizes the water so it stays clean during the off-season
What to Use:
Chlorine shock (calcium hypochlorite or sodium dichlor)
Non-chlorine oxidizers (for those using alternative sanitizers)
How to Use:
Add shock 1–2 days before closing the pool.
Make sure chlorine levels return to safe levels (1–3 ppm) before adding other chemicals or covering the pool.
⚖️ 2. Algaecide
Purpose:
Prevents algae blooms while the pool is covered
Helps keep water clear and clean until reopening
What to Use:
Polyquat algaecides are long-lasting and less likely to foam.
Avoid copper-based algaecides if you're concerned about staining or scaling.
How to Use:
Add after the chlorine shock has dissipated (usually 24 hours later).
Pour evenly around the pool, and let the pump run for at least a few hours.
⚖️ 3. pH Adjusters
Purpose:
Ensures the water is balanced to avoid corrosion, scaling, or damage during winter
Ideal Range:
pH: 7.2 to 7.6
What to Use:
pH increaser (sodium carbonate) if pH is too low
pH reducer (muriatic acid or sodium bisulfate) if pH is too high
How to Use:
Test the water before adding.
Adjust in small doses and retest to ensure it falls within the safe range.
⚖️ 4. Alkalinity Adjusters
Purpose:
Keeps pH stable over time
Prevents corrosion or cloudiness
Ideal Range:
Total Alkalinity: 80–120 ppm
What to Use:
Alkalinity increaser (sodium bicarbonate)
How to Use:
Adjust alkalinity before pH — it acts as a buffer to stabilize pH.
⚖️ 5. Calcium Hardness Increaser (if needed)
Purpose:
Prevents etching, plaster damage, or vinyl liner issues due to soft water
Ideal Range:
Calcium Hardness: 200–400 ppm
What to Use:
Calcium chloride
How to Use:
Only adjust if your water is too soft.
Add slowly and stir well to avoid cloudiness or scaling.
🧂 6. Stain and Scale Preventer
Purpose:
Prevents mineral buildup and metal stains during the off-season
What to Use:
Sequestrants or metal removers (phosphonic acid-based products work well)
How to Use:
Add after balancing water and before covering the pool.
⚠️ Optional: Enzyme-Based Cleaner
Purpose:
Breaks down organic materials like oils and lotions to prevent waterline scum
When to Use:
In pools that get heavy swimmer use or where contaminants are common
🧼 Final Water Balance Checklist Before Closing
| Chemical | Ideal Range |
|---|---|
| Free Chlorine | 1–3 ppm |
| pH | 7.2–7.6 |
| Total Alkalinity | 80–120 ppm |
| Calcium Hardness | 200–400 ppm |
| Cyanuric Acid (Stabilizer) | 30–50 ppm |
Always run your pump for at least 24 hours after adding all closing chemicals to ensure proper distribution.
🛑 Important Tips
Never drain your pool completely unless necessary and safe for your pool type.
Clean the pool thoroughly before closing — vacuum, skim, and scrub walls.
Lower the water level (about 4–6 inches below the skimmer) depending on your pool and cover type.
Blow out plumbing lines and plug them to prevent freeze damage in colder climates.
Install a good quality pool cover to keep debris out and maintain chemical balance.
Final Thoughts
Properly closing your pool with the right chemicals helps ensure that when spring rolls around, you're not dealing with green water, stains, or unexpected repairs. Taking the time now to balance and protect your water can save you hours of hassle and hundreds in maintenance costs later.
Would you like a printable pool closing chemical checklist or step-by-step closing guide next? ✅📝
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