I make up a hydro solution, and let it go for a week, yes, but I check pH daily if I'm around. if pH is off, I check EC. If EC is off, I correct. otherwise, I try not to fiddle with it too much. Remember EC will not tell you what is in there, only that it is in there to a certain concentration.
Retopping with nutes back up to a certain level, CAN, (not will) cause a toxicity in nutrients if the plants are not taking everything equally. And that they rarely do, but it is possible to harm your plants by doing this, so I just choose to change out every 2 weeks, or if they drink it all in a week, I change then.
hey m8 if you have a min a silly question 4 ya, got all my equipment together and seeds soaking now lol q, my friend tops his nutes up to 1.6 1.8 ec every day,is this correct i thought u make up formula leave for a week/10 days (hydro) and change water and re nute?i thought he would poison his plants this way but they seem to be loving it?