When people first evaluate HOCl dry misting, one number comes up fast: PPM. It sounds technical, and the instinct is often "more is better." With hypochlorous, that instinct is wrong — and understanding why is the difference between a protocol that works and one that wastes chemistry, risks the equipment, and delivers no extra benefit.
What PPM Actually Measures
PPM stands for parts per million — a measure of how much active ingredient is dissolved in a solution. For hypochlorous, the relevant figure is free available chlorine (FAC): the concentration of the active HOCl doing the work. A higher PPM means a more concentrated solution; it does not automatically mean a more effective one.
The reason is that HOCl doesn't work by brute force. It's an oxidizer that acts on contact, and its effectiveness in a real space is governed far more by coverage and contact time — whether the mist actually reaches every surface and stays in contact long enough — than by cranking up concentration. Past a certain point, extra PPM buys you nothing.
The Two Numbers That Matter: 294 and 300
GEIA protocols are built around two figures:
- 294 PPM — the target working concentration. This is the concentration GEIA systems are designed to run, and it's what the EPA-registered tablet dilutions are calibrated to produce. It sits in the effective range without overshooting.
- 300 PPM — the equipment maximum. This is a hard ceiling, not a suggestion. Running above 300 PPM offers no performance gain and can affect the equipment over time. Never exceed it.
That's why the dilution ratios are precise: one 3.3g Tablet per gallon of water, or one 6.5g Tablet per two gallons, each lands at 294 PPM. Following the tablet's EPA-registered label directions is what keeps you in the right window — the recipe is doing the concentration math for you.
How to Confirm You're in Range
You don't have to guess. FAC PPM test strips let you verify a mixed batch before you run it. Dip, read, and confirm you're near 294 PPM and under the 300 ceiling. It's a five-second check that turns "we think it's mixed right" into "we know it is" — worth building into any SOP, especially in facilities with documentation requirements.
One more practical note: mixed HOCl solution has a shelf life of about 24 hours. Potency declines after mixing, so mix what you'll use in a day rather than batching ahead. A day-old solution can read lower than 294 PPM even if it was mixed perfectly — another reason the test strip is your friend.
Dialing It In for Your Industry
The target concentration is consistent, but how you apply it varies by setting. A dental operatory, a hospital patient room, a kennel run, a cannabis flower room, and a food-processing anteroom all differ in volume, airflow, soil load, and how often they're treated. Those variables shape your protocol — cycle length, frequency, and room prep — not your PPM. Concentration stays at target; coverage and contact time are the levers you actually adjust, and airflow and pressure are the biggest factor in whether a cycle reaches the whole space.
This is also why pre-cleaning matters. Heavy organic soil consumes free available chlorine, effectively lowering the concentration that reaches the pathogen. Cleaning first isn't just protocol box-checking — it protects the very PPM you mixed for. Dry misting is a layer on top of cleaning, and clean surfaces let your target concentration do its job.
The Bottom Line
Concentration is a guardrail, not a dial to crank. Mix to 294 PPM, never exceed the 300 PPM equipment maximum, verify with a test strip, use the solution within 24 hours, and put your real effort into coverage, contact time, and pre-cleaning. That's how a protocol earns consistent results — and it's exactly what the tablet dilutions and equipment settings are engineered to make easy.
Want help building a protocol for your facility? See the Mixing & Maintenance guide, request a quote, or talk to your nearest GEIA distributor.