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CH255 PPM/pH Digital Controller
- Product Details
- Specifications
- Installation
- Operation
Free Chlorine and pH, Controlled Automatically
The CHEMTROL® CH255 keeps your pool or spa water balanced around the clock. It measures the free chlorine directly, in ppm, together with the pH, and switches your chemical feeders on and off as needed — clear, safe water without daily manual dosing.
CHEMTROL® controllers have been proven in pools around the world for more than 30 years. The CH255 is the set-and-forget choice for chlorinated residential and commercial pools and spas, hotels, health clubs and apartment buildings — and especially for outdoor pools that use stabiliser. Every setting is on the front panel, and the electronics carry a 5-year warranty.
Key Features
- Shows and controls true free chlorine in ppm — the figure your test kit gives
- Not affected by cyanuric acid stabiliser, at any level
- No reagents to buy and no pressurised cell
- Doses acid or alkali for pH — set once to suit your chlorine
- Safety interlock stops dosing if the pH goes out of range
- Proportional feed eases off as each reading nears its set-point, so small pools and spas are not overdosed
- Separate overfeed safety timers and high and low alarms, with a remote alarm output
- Every setting clearly labelled on the front panel, and kept through power failures
- 5-year electronics warranty; 2-year warranty on the free chlorine sensor
True Free Chlorine Readings
The free chlorine sensor reads free chlorine directly, in ppm (parts per million, the same as mg/L) — the same figure your DPD #1 test kit gives, not an estimate worked out from ORP.
Its big advantage is that cyanuric acid stabiliser does not throw it off, at any level. In outdoor pools, stabiliser makes ORP readings fall even when there is plenty of chlorine; the CH255 keeps reading, and holding, the true free chlorine level. The solid-state sensor needs no reagents and no pressurised cell, and it carries its own 2-year warranty.
Need 4–20 mA outputs for a building management system or chart recorder? See the CH265.
CH255 Specifications
| Item | CH255 |
|---|---|
| Controls | Free chlorine (ppm) and pH |
| Sanitiser set-point | Free chlorine 0.1 to 10 ppm (factory setting 1.0 ppm) |
| pH set-point | 4.5 to 9.5 (factory setting 7.5) |
| Display range | Free chlorine 0 to 10 ppm; pH 0 to 14 |
| Accuracy | Free chlorine 0.1 ppm; pH ±0.1 |
| Readouts | Digital LED readouts, ppm (3 digits) and pH (2 digits); indicator lights for feed mode, feed status and alarms |
| Free chlorine sensor | Solid-state, selective membrane, 0 to 10 ppm; not affected by cyanuric acid. Low-range (0 to 2 ppm) and membraneless (salt chlorinator) sensors available |
| pH sensor | Glass electrode with 3 m cable |
| Feed modes | Off, manual or automatic; on/off or proportional feed |
| pH feed | Acid or base, selectable |
| Outputs | Chlorine feed and pH feed, each 5 A at supply voltage |
| 4–20 mA output | Optional |
| Alarms | High and low out-of-range alarms and overfeed alarms; audible, visual and remote (powered or dry contact) |
| Safety | Separate overfeed safety timers, sanitiser/pH interlock, diagnostic self-test, safety flow switch input; settings kept through power failures |
| Plumbing | Flow cell assembly with strainer, on a bypass line |
| Cabinet | Polystyrene, rain- and splash-proof, with clear window cover, 22 x 18 x 10 cm |
| Electrical | 230 VAC or 24 VAC (please specify when ordering); draws 0.25 A, excluding feeders |
| Warranty | 5 years on the electronic module; 2 years on the free chlorine sensor; 1 year on other parts |
Need a hand choosing sensors, plumbing or dosing pumps? Call us on 1300 585 820.
CH255 Installation
The CH255 is simple to install: there are no reagents to buy and no pressurised cell to fit. The free chlorine sensor and the pH sensor sit in flow cells on a small bypass line, as the diagram shows.
Controller
Mount the controller on a wall in a secure spot, out of direct sun and away from stored chemicals, at least 3 m from the water’s edge and close to the sensors. Wire it to the pump timer, in parallel with the circulation pump, so it can only dose while water is flowing. A qualified electrician should make the connection, following local wiring rules.
Sensors and Flow Cell
Take the bypass line from after the filter, through a strainer, to the Flow Cell Assembly. The clear cell lets you see the sensor tips, has a tap for taking water samples, and a bleed to stop air locks. Aim for a gentle, steady flow past the free chlorine sensor of 20 to 100 litres an hour, ideally about 30 litres an hour. Fit a safety flow switch on the bypass line, so no chemical is fed if the line is shut or blocked.
Before first use, soak the free chlorine sensor in lightly chlorinated water for 30 to 60 minutes, without connecting it to the controller. After start-up, check it against a DPD #1 test kit at 2 hours and again at 24 hours, and calibrate if needed.
Chemical Feeders
Connect the chlorine and the acid (or alkali) dosing pumps to the controller, and inject the chemicals downstream of the sensors and of the filter and heater. For a chlorine erosion feeder, fit a corrosion-resistant solenoid valve on the feeder’s intake line. For pools with a salt chlorinator, a membraneless free chlorine sensor is available.
CH255 Operation
Once set up, the CH255 runs itself. Every function is labelled on the front panel, and the two readouts show the free chlorine and pH at a glance.
Factory Set-points
The free chlorine set-point comes set at 1.0 ppm, the level recommended to kill germs and bacteria and keep the water in good condition. Set it to suit your state health department’s requirements for your pool.
The pH set-point comes set at 7.5. At 7.5 the water is comfortable for swimmers and the chlorine works well. Below 7.4 it causes eye irritation and corrosion of equipment; above 7.6 it also irritates eyes, and leads to cloudy water, scale, stains and weaker sanitiser.
These are factory defaults, not fixed values: the operator can change them at any time to suit the water and local health requirements.
Changing a Setting
Press SETPOINT, then PPM or pH — the display flashes. Use the up and down arrows to reach the value you want, then press SETPOINT again to save it. The alarm limits, the safety timers and the calibration are changed the same way, with their own buttons. To choose a feed mode, press PPM or pH until the Off, Manual or Auto light comes on.
Test the water regularly with a DPD #1 kit for free chlorine and a phenol red kit for pH. If the controller reads differently, press CALIBRATION, then PPM or pH, adjust with the arrows, and press CALIBRATION again.
When first switched on, the controller shows its set-up menu: acid or base feed for pH (acid is the default, for liquid or granular chlorine; base is for trichlor tablets), the sanitiser/pH interlock, and the safety flow switch. Press both arrow buttons together to see it again at any time.
Alarms and the Safety Timers
Each reading has high and low alarm limits (from the factory, 0.3 to 6.0 ppm for free chlorine and 7.0 to 8.0 for pH). If the chlorine is low, the red alarm light flashes and chlorine feed carries on so the water can recover. If the pH goes out of range, the alarm flashes and dosing stops until it is put right — chlorine works poorly at the wrong pH. This sanitiser/pH interlock can be switched off in the set-up menu.
The overfeed safety timers guard against an empty drum, a failed pump or a blocked line. They are factory set at 15 minutes for chlorine and 5 minutes for pH, normally plenty to reach the set-point. If a feeder runs longer, the controller stops it, turns on the alarm and flashes the overfeed time. Once the cause is fixed, switch the feed mode to Off and back to Auto to reset the timer.
Back to Factory Settings
Your settings are kept in memory, even through a power failure. To return a set-point and calibration to the factory values, hold the PPM or pH button for 5 seconds.
