Chemical DosageIntermediate 28 min read

Chemical Dosage: Process Control Basics

Turning a target dose into an actual pump or feeder setting: liquid chemical feed rate math using percent strength and specific gravity, dry chemical feeder settings accounting for purity, and rearranging the pounds formula to solve for dose or flow.

Knowing you need "41.7 lbs/day of chlorine" doesn't tell a pump operator anything useful — pumps are set in gallons per day, not pounds. Bridging that gap between a pounds-per-day target and an actual feeder or pump setting is where dosage math becomes real process control, and it's the math tested at every mid-level operator class across every discipline in Colorado.

The Problem With Real Chemicals

The pounds formula,

lbs/day = mg/L \times MGD \times 8.34

, gives you pounds of pure, 100%-active chemical. But almost nothing an operator feeds is 100% pure:

Liquid sodium hypochlorite is typically sold at 10–12.5% available chlorine, not 100%.
Dry calcium hypochlorite is typically 65–70% available chlorine.
Liquid ferric chloride is often sold as a 35–42% solution.
Commercial dry chemicals (soda ash, lime, polymer) are rarely 100% pure product.

So the real-world question

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