To make a 150 ppm peracetic acid (PAA) solution, add 0.2–0.4 oz of a 5% concentrate or 0.13 oz of a 15% concentrate per gallon of water.
Understanding the concentration numbers
PAA is sold as a liquid with an active percentage. A 5% concentrate means 5 g of PAA per 100 mL of solution, while a 15% concentrate contains three times that amount. The dilution factor is directly proportional to the concentration.
Calculating the dose for 150 ppm
150 ppm equals 150 mg of active PAA per litre of finished solution. Because 1 oz ≈ 28.35 g, 0.2 oz of a 5% concentrate provides about 5.7 g of PAA. Dividing 5.7 g by 28.35 L gives roughly 200 ppm, which is close enough for most sanitising purposes. A 15% concentrate needs only 0.13 oz to reach the same ppm.
Adjusting for water quality
Hard water (high carbonate hardness) neutralises some PAA, so a 5–10 % dose increase may be needed. Alkaline water (pH > 8) can also reduce effectiveness. If the water is very soft and neutral, the standard dose is usually adequate.
Temperature and stability
PAA degrades faster in warm water. Keep the solution between 50–70 °F to maintain potency. If the water exceeds 120 °F, the active concentration can drop below 100 ppm before the sanitizer contacts the surface.
Common pitfalls to avoid
- Mixing a 5% and a 15% concentrate in the same batch.
- Using a larger volume than the calculated dose for the same ppm target.
- Ignoring the organic load; pre‑cleaning is essential to keep the sanitizer active.
- Relying solely on test strips that do not account for temperature or pH.
When higher concentrations are needed
For non‑food contact surfaces or shock treatments, 500–1000 ppm may be required. That translates to roughly 1.1–2.2 oz of a 5% concentrate per gallon or 0.7–1.4 oz of a 15% concentrate. Use protective equipment and ensure the area is well ventilated.