An ex colleague of mine used to design all the electronic circuits for the control on the plant. He designed the following circuit, which was used for sump pump level control.
The probes were made out of 5mm Stainless steel rods placed in a triangular fashion about 1” (25mm) apart. The only problem we had with the probes was that the sumps was often filled with mud, and that started a buildup on the probes. The top of the probe assembly (where the wires are connected to the probes) was always kept way above the high level water mark.
I attach his circuit. It has less components than the one you’re currently using. If I can recall the operating voltage was 24V DC. X-1, X-2 and X-3 are the three probes for the level detection. The common probe (X-1) is as long, or even longer than the Low level (X-3) probe.