Alright man, I just read your question. Look, this may sound mean and in all actuality I am not trying to be mean but I am telling you the way it is going to be. You asked how your plant looked yesterday. I said fine, now 24 hours later you are asking how your plant looks again. Look bro, we aren't going to tell you every day that your plant looks fine. I don't mind helping out if you have problems along the way as most everyone here will do. But if you are going to ask everyday how your plant looks then send her to me and I will grow her.
Now, as for your question about the nutrients. Yes, use the amount that it takes and put the rest back. I normally put an airstone in my nutrient mixture to keep them oxygenated while they are waiting to be used. Make sure you recheck the ph right before you get ready to use them as they will change over the course of a few days. If you don't use them in a week I would toss them. No reason really, I just don't want mine exposed to air for that long. It has a tendency to get serratia marcescens bacteria.