There are a number of companies that make electronic probes for water testing. I have looked at a number of them for PH and Nitrate testing especially.
Here are a few popular vendors:
Welcome to American Marine Inc.
I found that the meters are pricey, many need to be calibrated on a regular basis, and the replaceable probe that goes in the water can dry out or be damaged if not properly cared for. They also cannot be left permanetly monitoring your tank.
I have seen meters on clearance at a number of online shops so I am guessing that they did not sell very well for those reasons.
I gave up looking and just kept on using liquids..................