Top off res with nutrients or just water?

[RUKind]

my plants are drinking a lot and i use an aeroflo system as well...i top off w/ plain water following the golden principle of "underfert is better than overfert"....at least your plants wont die and you can observe them and add nutes if they show any deficiencies (mine never have)

[fhydro]

Well, the problem is more simple i think. If the water level drops with the ppm level, putting plain water would drop the ppm level as much. So, except if there is nearly no water, you must consider the problem, but if the PH is good and only the ppm level drops ( and water a little also ), don't do nothing. Yes, one thing, change the nutes avery week. I add water only in case of PH problem ( low PH ). During one grow, i added normal mix of nutes to top off the rez ( summer, heat, evaporation ) and i had a serious over fert problem. I think that the ppm dropping means only that they eat the nutes.
Fhydro