Oh I add new solution all the time, the plants drink obviously. It's just you only have to do that a few times in veg and then either change water or just add more in most cases, if there's no need to care for algae or some shit. In flower I refill the tank a couple of times a week. Then the last weeks I just give water.

Oh, I don't know about mixing nutes. They might have crazy chemistry and different balances and whatnot. Or do you mean mixing the solutions, right? Probably better, but I've never done it though. I'm not saying there's a risk. I'm just not aware and there might be, because I don't know since I've not looked into that. Depends on the complexity of your nute line I guess. Some have all kinds of crazy chems to buffer PH and whatnot.

oh remember to try and cover any holes going down to the where nutes rune so you keep algae off as long as possible. i have h2o2 that I use to countermand it but it was a problem this grow and has been a few grows for me.

But it's a weed, just don't be too rough and it'll be fine