Why Draining Is Sometimes Necessary
In Arizona’s hot and arid climate, pool water doesn’t get replaced as often as in other regions. That leads to gradual buildup of chemicals like cyanuric acid (CYA), calcium hardness, and total dissolved solids (TDS)—each of which can cause long-term issues:
- High CYA reduces chlorine effectiveness.
- Elevated calcium leads to scale buildup and cloudy water.
- Excessive TDS can interfere with water balance and clarity.
When levels climb too high, chemical adjustments won't fix the issue. The solution? A partial drain and refill—but it’s important to calculate how much water to drain to hit your target levels.
The Formula: Partial Drain Calculation
To determine the correct percentage of water to drain and replace, use this simple formula:
Drain Percentage (%) = (Current Level - Desired Level) / Current Level × 100
This tells you what percentage of the pool needs to be replaced with fresh water to achieve your desired chemistry.
Step-by-Step Example
Let’s say you test your pool and find the following:
- CYA (Cyanuric Acid): 180 ppm
- Desired CYA level: 60 ppm
Step 1: Use the formula:
(180 - 60) / 180 × 100 = 66.7%
Step 2: Your pool is 15,000 gallons. Multiply:
15,000 × 0.667 = 10,005 gallons
➡️ You should drain and replace approximately 10,000 gallons to reduce CYA to 60 ppm.
Same Approach Works for Calcium and TDS
You can use this formula to reduce calcium hardness or TDS as well. Just plug in the current and target levels:
Calcium Example:
- Current CH: 800 ppm
- Desired CH: 400 ppm
→ Drain 50% of your pool water.
TDS Example:
- Current TDS: 3,000 ppm
- Desired TDS: 1,500 ppm
→ Drain 50% of your pool water.
Important Tips
- Test after refilling. Dilution may not be perfect—always retest levels after refill.
- Use a sump pump safely. Avoid draining below the skimmer unless you're using a submersible pump.
- Never fully drain a pool unless absolutely necessary and under professional guidance—especially plaster pools.
- Schedule during cooler weather to reduce surface stress during a drain.
We Can Handle It For You
Not sure how to safely drain and refill your pool? Founder's Pool Service offers partial draining services with expert water testing, high-efficiency pumping, and eco-friendly refills.
📍 Serving Buckeye, Verrado, Goodyear, and beyond.
Call Today for Help With High CYA, Calcium, or TDS
Let us handle your pool chemistry the right way—from testing to treatment. Call us or request a quote online.
