The step between chemistry decisions and actual water quality is the chemical feeder. It's the automation layer: sensors measure, controllers decide, feeders act. If the feeder drifts out of calibration, your water drifts with it — regardless of how good the upstream logic is.
The five common feeder types
1. Erosion (tablet) feeders
Tablets of trichlor or BCDMH (bromine) sit in a flow-through chamber and slowly dissolve as water passes. The rate is controlled by an adjustable flow valve.
- Pros: Cheapest to install, no electricity needed, simple
- Cons: Slow to respond to changing demand, adds CYA continuously (trichlor), no precise dosing
- Typical use: Small residential, spas, light commercial
2. Peristaltic (hose pump) feeders
A rotating pump head squeezes a flexible tube, pushing precise amounts of liquid chlorine or acid. Output is rate-proportional to motor speed.
- Pros: Precise dosing, handles corrosive liquids well, can be controller-driven
- Cons: Tube wears and needs replacement every 6–12 months, limited pressure capability
- Typical use: Residential automation, small-to-medium commercial
3. Diaphragm / piston feeders
A motor drives a diaphragm or piston that pushes precise volumes per stroke. More pressure capability than peristaltic.
- Pros: Higher pressure, more reliable at high flow, accurate
- Cons: More maintenance, check-valves can foul, more expensive
- Typical use: Mid-to-large commercial
4. Gas chlorine systems
Compressed chlorine gas is drawn by vacuum through a regulator and mixed into the circulation line. Extremely efficient per pound of chlorine, but requires a dedicated chlorine room with scrubbing and OSHA-compliant safety.
- Pros: Very low per-pound cost, no CYA added, no pH side effects from carrier
- Cons: High-risk hazmat, regulated by local fire code, specialized training required
- Typical use: Large public aquatic facilities, water parks
5. On-site generation (salt chlorine generators)
Electrolysis cell converts dissolved salt (NaCl) into hypochlorous acid. The pool itself is the chlorine factory.
- Pros: Low-maintenance, no chemical storage, consistent output
- Cons: High pH drift, cell scaling (especially in hard water), cell replacement every 3–7 years at ~$700–1,200
- Typical use: Residential, small commercial
Feeder maintenance basics
- Erosion feeders: Clean the chamber quarterly. Inspect O-rings. Never mix different sanitizer types in one feeder.
- Peristaltic: Replace tube at manufacturer interval or at first sign of cracking. Confirm prime at each service.
- Diaphragm: Inspect check-valves monthly. Calibrate output quarterly with a graduated cylinder.
- Gas: Annual service by licensed technician. Scrubber maintenance and emergency-equipment checks per fire code.
- Salt cells: Acid-wash every 3–6 months in hard-water regions. Replace at 3,000–10,000 running hours depending on model.
Calibrating a feeder
Every feeder should be calibrated on install and verified annually:
- Draw a measured volume from the source tank (say, 1 gallon).
- Run the feeder at a known setting for a timed interval (say, 10 minutes).
- Measure the volume actually delivered.
- Compare to the manufacturer's rated output.
- Adjust the feeder setting or flag for service.
Mixing chemicals — the inviolable rule
Neverconnect an acid feeder and a chlorine feeder to the same injection point. Even a few seconds of back-flow can mix sodium hypochlorite with muriatic acid, releasing chlorine gas. Separate injection points with at least 18 inches of pipe run and a check-valve on each. In commercial systems, put acid feed upstream of chlorine feed so they can't collide on a pump shutoff.