Automatic chlorinators hold a supply of slow-dissolving chlorine tablets and meter chlorine into the pool water at a controlled rate. They provide consistent dosing between maintenance visits.
Key Facts
- Inline feeders are plumbed into the return line after the pump and filter; offline feeders bypass a small amount of flow.
- Trichlor tablets (3-inch or 1-inch) are the standard product for automatic feeders.
- Feed rate setting affects how much chlorine dissolves per day — adjust based on pool volume and actual FC readings.
- Never put chlorine tablets directly into the skimmer — the concentrated acid from dissolving tablets can corrode equipment.
How Automatic Feeders Work
Inline feeders are installed in the pool plumbing between the filter and the pool return. Pool water flows through the feeder housing, over the slow-dissolving tablets, picking up chlorine as it passes. The feed rate is typically adjusted by a dial that controls water flow through the feeder — more flow equals faster tablet dissolution and more chlorine released. Offline (bypass) feeders connect to the plumbing with a small bypass valve that diverts a fraction of the return flow through the feeder. They are easier to install in existing systems. Both types achieve the same result: continuous low-level chlorine dosing between maintenance visits.
Setting the Feed Rate
The correct feed rate depends on pool volume, sun exposure, bather load, and current CYA level. Start at the mid-range setting, run the system for 24–48 hours, and test free chlorine. If FC is below target (1 ppm), increase the feed rate. If FC is above 3 ppm consistently, decrease it. Never set and forget — seasonal changes require adjustments. In summer with heavy UV and bather load, the feeder setting for early spring will likely under-dose. In autumn with low use, the same setting will likely over-dose.
Compatibility Considerations
Trichlor tablets are strongly acidic (pH approximately 2.8) and contain cyanuric acid. Every time a tablet dissolves, it lowers pH and adds CYA. In a pool managed exclusively with a tablet feeder, CYA can reach problem levels (80–100 ppm) within one season and pH will consistently trend low without acid addition. Test pH and CYA monthly when using an automatic feeder. Never mix different types of chlorine products inside the feeder — trichlor and cal-hypo in contact can react violently. Empty and rinse the feeder before switching products.
Examples
As the season winds down, a pool owner discovers their CYA is at 85 ppm — above the 80 ppm upper limit. Review of maintenance records shows the feeder has been running at the same setting since spring. The summer bather load has been high (kids off school), and the feeder has been running at 100% feed rate, dissolving tablets quickly. The fix for next season: test CYA monthly and plan a 25% partial drain at mid-season to dilute CYA before it reaches problem levels. Switch to liquid chlorine for supplemental dosing in high-use periods to avoid adding more CYA.
Common Mistakes to Avoid
- Putting chlorine tablets directly in the skimmer — this creates a concentrated acid bath that corrodes equipment downstream.
- Not adjusting the feed rate seasonally — the same setting will over-dose in spring and under-dose in midsummer.
- Letting the feeder run empty for extended periods — the pool receives no chlorine and can develop algae in the time between feeder refills.
- Pool & Hot Tub Alliance — Pool & Spa Operator Handbook, 2022