The best pH meter for water based paints and any viscous fluids is the Mettler Toledo FiveGo pH meter coupled with the EpoxyTough flat ended pH electrode.
Mettler Toledo FiveGo pH meter
The FiveGo meter is a small and easy to use handheld meter. It can display pH and temperature simultaneously, and can fit any electrode with a standard BNC connection.

• Automatic buffer recognition
• Automatic temperature compensation
• Simultaneous pH and temperature reading
• Storage of up to 30 results
For technical specifications click here.
Camlab EpoxyTough Flat End pH Electrode
Camlab EpoxyTough pH electrodes are tough epoxy bodied combination with a gel filling so you never need to worry about electrode maintenance or refilling again. They are compatible with nearly every pH meter straight out of the box or with a simple adapter cable. Standard models feature an extended body which protects the sensitive pH sensing bulb. You can even use an EpoxyTough to stir your sample with to get a fast stable reading.

Available in single or double junction designs, spear tip, flat surface, micro and extended body versions, there is a Camlab EpoxyTough electrode to suit your requirements.
The ExpoyTough flat double junction combination electrode provides added protection for contamination of the reference, providing a longer life. This robust and easy to clean electrode is ideal for measuring hard to clean fluids and for low volume pH measurement.
The probe will need proper maintenance and cleaning with the correct cleaning solutions. Camlab can also supply cleaning solutions to remove proteins, sulphides and organic components from the probe to ensure optimal performance.