When changing the weekly water, do you refill the ...

You need a certain amount of nutrients in the water so a certain level of ppm/ec. When you add plain water you are lowing that level ( not good ) so when you are refilling your tank you need to reach a certain ppm/ec level ( so you add nutrients)

Couple different ways you can do this, but I wouldn't mix the nutrients prior to them going into your water.. they are in separate bottles mainly due to how they are chelated.. or how the ions and molecules are bonded together (your nutrients N,P,K etc)... so you want them to be in some water before you mix them. Each nutrient company has their own preferred method/order of mixing nutrients, but typically you add your micros first (cal-mag, armor si's) then your macros (N,P,K). For example, Armor Si (silica) suggests you wait 15 minutes before adding in any other nutrients... as it doesn't react well initially with high PH or high PPM solutions. You should change out your nutrients every 1-2 weeks.. I like to do it every 7-10 days. If you have a separate reservoir, then it's much easier because you can fill that reservoir, and just swap them out with the new fresh nutrient solution. If not, you have to remove all the water manually and make sure you give your reservoir a wipe down/cleaning, Calcium and salts will build up on the bottom of your reservoir... clean the air-stones and airlines too. If you remove the water manually, I suggest filling the reservoir halfway-75%.. adding your nutrients, 1 at a time, then topping the reservoir off. Filling the reservoir to ~75% allows some room for error as well, so if you add too much feed and your PPMs are higher than your target PPMs, you can easily dilute your reservoir. Also, you should definitely make sure you reservoir is light proof... cover those holes! Light getting to your water is 1 of the worse things for hydro growers.. you will get root rot, algae build up, high water temps, and the roots don't particularly like light either. Don't be afraid to send me a message if you have any other questions... I will try to help the best I can 😁. good luck and happy growing!