30 gallon tanks are cheap, and even installed shouldnt be 600 bucks.

if the control is bad I would replace the tank and get at least a 40
gallon tank.

have you priced home depot or lowes for tanks?

with real hard water the tank may be filled with sediment, when
heating it will make a boiling noise.

I would replace the tank going larger like 50 gallon maximizes the
time till it flls with crud again