as an example:
Start of week, fill res to lets say 400ppm
next day water level dropped and ppm's are at 450 <- They rose 50ppm in 24 hours, means i should probably make res around 350 so i top off and get ppm's to 350ish.
Next day ppms are still 350ish and water level dropped <- this is perfect, stay here until it goes up or down.
next day same thing, just maintain water level and ppm around 350
next day ppms are at 300 <- ppm's went down 50ppm in 24hrs, top off res and bring ppm's up to about 400.
next day ppm's are still 400 and water level dropped <- perfect again, just maintain water level and ppm's
next day ppm's are 350 and water level dropped <- dropped 50ppm in 24hrs, top off and raise ppm to around 450
next day ppm's are 475, raised 25 in 24hrs <- top off and lower ppm's to around 425
next day ppm's are 420, dropped 5ppm <- this is still fine, top off and maintain ppm's at 425
next day ppm's are 400, dropped 25ppm <- top off and raise ppm to 450
rinse and repeat. I check ph and ppm every morning and every night and i write down the values each time and go from there.
edit: don't forget: somewhere in there you would empty the whole reservoir and fill it up again, every 1-2 weeks should be full res drain and refill.