I am experimenting at home with the idea of making an optical pH sensor that can read the colour of pH indicator using photodiodes.
I am wondering if there is some kind of ion permeable membrane that could be used to contain the indicator solution, so it can 'read' the pH of the solution being tested, without mixing with it.
I would like something that is fairly easily obtainable to me as a home experimenter.
The sensor could possibly be used make an automated pH corrector for my local aquaponics farm.
I looked into commercially available pH sensors. The glass bulb type and ISFET type suffer from drift and need regular calibration. There are optical types available, but they are too expensive for me.