One of the easiest ways of reducing EC change over time is to increase the nutrient volume. Doubling the volume will cut the EC change in half, doubling it again will cut it to a quarter, etc. Not sure if this is possible in your situation but just a suggestion.

never increasse nutrient levels above the labels instruction you risk burning the plant. also plants eat light not nutrients. you add them to help facilitate photosynthesis. top off the system with water and flush once every 5-10 days. Nutrient solutions is cheap recyclings a pain. pH is the only thing that must stay constant to prevent precipitants from the solution. Email me for info on where to get a good pH meter (it has to be double junction for hydroponic or else it won't work for long)