The only time I. Don't change the res is when I'm using a one gallon amount of solution. The reason is because the plant soaks it all so fast that there litterally is nothing to change, all the water goes into the roots, but then ofcourse you have to be refilling it immediately before the roots dry. If you use, an. Any method though you should still be wiping the res with towel before refilling. I recommend just about filling your res with water and nuts half way at all times, as the water level goes down every or every other day add more to get it back to half way but never over, then on your last day to two days don't add anymore before a flush. Then once flushed keep adding water daily to keep it half way. Personally I use a commercial 112 litters a minute pump with 5 air stones for my res so I have one on each corner and one in the middle so my water is very well oxygenated and I notice the water and nuts get soaked up more then when I had only one air stone with a smaller pump, so I fill my res to the top but unless you have a huge loud pump like mine I would stick to low water levels of half way to avoid changing the flush so much and wasting nutes.
