• ReefSense pH & Temperature Probe – R35821
• 2 calibration solution sachets (pH 7 and pH 10)

A probe holder and a calibration vial are not included. You’ll need a probe holder to position the probe in your aquarium or sump – the ReefSense single probe holder (R35837) or the ReefSense magnetic probe holder (R35826) – and a small clean container to hold the solution when you calibrate.

Position the probe in the aquarium or sump where there is good, steady water flow, using a probe holder, with the glass membrane at the tip fully immersed at all times. Avoid spots with trapped air or heavy detritus. The ReefSense single probe holder (R35837) is an optional accessory for positioning the probe.

1. Remove the storage cap before use. The probe ships with a storage cap – held on by a compression fitting – that keeps the glass membrane wet and stops the storage solution leaking during transport and storage. Take it off before installing the probe. Keep the cap: you can refill it with storage solution to keep the tip wet if you ever take the probe out of service.
2. Fit the probe into your probe holder and position it in the water with good flow around the tip.
3. Connect the probe to the ReefSense port connector cable, making sure the securing nut is fully closed for a stable, waterproof connection.
4. Arrange the cable into a drip loop so water can’t run down it to the connector.

Add the probe to your ReefControl Pro/Lite in the app:
1. Open your ReefControl Pro/Lite in the ReefBeat App and choose Setup Probe, then select pH & Temperature.
2. The app shows the ID of the probe it has found so you can confirm you’re setting up the right one, then continue. (If the app doesn’t detect the probe, check the connection and try again.)
3. If a newer version of the probe’s firmware is available, the app updates it before continuing over Bluetooth – keep your phone within approximately 3 m (10′) of the probe and leave the app open during the update.
4. Give the probe a name, or keep the default.
5. Set the parameter ranges for pH (and for temperature), and choose whether to switch on the audible alarm for this probe.
6. Calibrate the probe now or later (see Calibration).

Parameter ranges (Desired / Acceptable / Danger). For each parameter you set two ranges that tell ReefControl Pro/Lite what “normal” looks like for your tank: a Desired range (green, your target) and an Acceptable range (orange, drifting away from the target). Anything outside the Acceptable range is automatically the Danger range (red) – you don’t set this yourself. Your readings show against these on the homepage and in the graphs, and you can choose, for each parameter, to be notified when a reading enters its Danger range. You can also switch on the audible alarm; it is then enabled whenever a reading is outside the Acceptable range, and a short press of the Manual Control button silences it.

A pH probe measures a tiny voltage on its glass membrane that is proportional to the pH of the water; calibration defines how the probe turns those millivolts into a pH value. The sensing element ages gradually with use, so its readings slowly drift – calibrating corrects for this and keeps your readings accurate. For a reef aquarium, recalibrate about once a month.

The probe is digital, so the ReefBeat App guides you through the whole process and the probe calibrates itself and stores its own calibration data, reporting back as each point succeeds. With good care a ReefSense pH Probe lasts up to about 12 months of continuous use; it monitors its own condition and the app lets you know as it nears the end of its life.

What you need

The pH 7 and pH 10 calibration sachets supplied with the probe, a small clean container to hold each solution, and some RO water for rinsing. Always use fresh solution and don’t reuse solution the probe has already been in – contaminated solution gives a false calibration.

Calibration points

For a reef (marine) aquarium, with a pH around 8, calibrate at pH 7 and pH 10 – the two solutions supplied – and both points are needed for a correct calibration. (On a freshwater aquarium you’d calibrate at pH 4 and pH 7 instead. Red Sea doesn’t supply a pH 4 solution, but pH 4 calibration solutions are widely available – just choose the matching solution from the list in the app.) In the app, solutions are grouped into Low, Mid and High ranges – for a reef tank you’ll use the Mid (pH 7) and High (pH 10) solutions.

The calibration process

The ReefBeat App guides you through each step:
1. When prompted, clean the probe, rinse it with RO water and dry it – this stops residue from contaminating the solution. Dry only the outside of the probe; do not wipe the glass membrane, as this can damage it and make readings unstable.
2. Place the probe in the first solution and gently wiggle it to release any air bubbles trapped against the glass membrane, then select the exact solution you’re using from the list.
3. When you start the calibration, the probe stabilises for about three minutes and records the point automatically. (If you prefer, let it sit a few extra minutes for analytical-grade accuracy that reef monitoring doesn’t normally need.)
4. The app shows the measured pH of the solution so you can confirm it looks right. If a reading falls outside the expected range for that solution, the app tells you so you can rinse and try again.
5. Rinse and dry the probe, then repeat for the second solution.

The first calibration

Your probe is calibrated at the factory, but after time in its storage solution between manufacture and installation it should be recalibrated before you rely on it. Install it, let it run for a few hours to settle, then calibrate.

Calibration solutions and temperature

pH calibration solutions are precise buffers whose own pH changes slightly with temperature, so each has a nominal pH quoted at a reference temperature – Red Sea’s are pH 7.00 and pH 10.00 at 25 °C. The ReefSense pH Probe has these relationships built in: using its internal temperature sensor it knows the true pH of the solution at its current temperature and calibrates to that automatically – something a typical hobby pH meter can’t do.

One result is worth knowing in advance: at the end of calibration the app shows the solution’s actual pH at its current temperature, which may differ slightly from the nominal value on the sachet. This is correct. The difference is tiny for pH 7 but more noticeable for pH 10 – for example, a pH 10.00 (at 25 °C) solution that is actually at about 20 °C reads about 10.06, its true value at that temperature.

Actual pH of the calibration solutions at different temperatures:

Calibrating at a sink (remote mode)

You can also calibrate the probe away from the controller, over Bluetooth, which is often more comfortable than working down beside the sump – see Remote mode for how to set this up.

Temperature

The probe also reports your water temperature, with its own ranges, log and control options, and it uses that temperature internally to compensate the pH reading. Because of this, the app offers a Temperature Calibration option rather than a simple offset: changing it also changes the pH value, so only adjust it with a high-precision laboratory temperature reference – otherwise leave it at the factory calibration.

You can use the pH Probe away from the controller, over Bluetooth – handy for taking a reading or calibrating at a sink rather than working down beside the sump. In remote mode the probe can be used for manual readings and for calibration.

1. Turn on remote use for the probe in the ReefBeat App.
2. Disconnect the probe from the ReefSense port connector.
3. Power the probe with the ReefSense USB-C connector (sold separately), plugged into any USB-C source.
4. In the app, tap Connect to start the Bluetooth (BLE) connection between the app and the probe.

When you’ve finished, you can tap Disconnect in the app, or simply remove power from the probe – once the probe is unpowered it disconnects automatically. Keep the glass membrane in water throughout. After returning the probe to the aquarium, wait about 30 seconds before cancelling remote mode in the app, to keep stray readings out of your logs.

From time to time the ReefBeat App will let you know that a firmware update is available for your pH Probe. Keeping the firmware up to date ensures it stays compatible with the app. Firmware updates are performed via Bluetooth; the probe must be connected to your ReefControl Pro/Lite and not in Remote mode (ensure Bluetooth is enabled in your phone’s settings). When you run an update, keep your phone within approximately 3 m (10′) of the probe and leave the app open during the update.

Your pH reading can switch equipment on and off automatically – for example, controlling the CO₂ solenoid on a calcium reactor so it eases off if pH drops too low, or triggering other pH-linked equipment. The pH Probe can control a 12 VDC port on the controller, or – if you have a ReefControl Power – any of its AC sockets.

Set the relevant port or socket to be controlled by the pH Probe, choose the value at which it switches, and set a fallback state in case the probe is ever disconnected. (See your ReefControl Pro/Lite manual for how to assign a port or socket.)

The pH & Temperature Probe needs a little routine care to stay accurate, and its glass membrane is delicate, so handle it gently.

Keep the membrane hydrated. Never let the glass membrane dry out. If the probe is out of the water for more than a short time, keep the tip in storage solution or aquarium water. A dried-out membrane reads slowly and unstably.

Cleaning the probe

Keep the glass membrane clean so your readings stay accurate – but treat it gently. Never wipe, rub or touch the glass bulb at the tip: rubbing scratches the surface and builds up a static charge, both of which make readings slow and unstable. Clean by rinsing and soaking only.

Routine cleaning. Rinse the probe under RO water to remove salt and loose film. Do this each time you calibrate (about monthly), and whenever readings begin to look sluggish or drift.

Removing stubborn fouling. If organic film or mineral deposits have built up, clean in two stages, rinsing well with RO water between and after each stage:
1. Remove organics first with a diluted, plain (unscented) household bleach solution – 1 part bleach to 10 parts RO water. Soak the tip for 2-5 minutes, then rinse thoroughly with RO water.
2. Then remove mineral deposits with Red Sea’s probe cleaning solution (R35855), a weak acid, diluted 1:10 with RO water. Soak for 2-5 minutes, then rinse thoroughly with RO water.

Rehydrate and recalibrate. After cleaning, rehydrate the membrane for at least 30 minutes – in KCl probe storage solution if you have it, or in freshly mixed seawater if not – then recalibrate before relying on the readings.

You can do cleaning and calibration comfortably at a sink in remote mode (see Remote mode).

It’s a wear part. The sensing element has a limited service life (up to about 12 months of continuous use). The probe tracks its own health and the app warns you as it ages, so you can replace it before readings become unreliable.

Press here for the Troubleshooting guide for the full ReefControl Family