I may catch some flac about it. But on my most recent grows I haven't change the reservoir throughout the entire flower cycle and honestly I can't see it hurting anything. My last plant brought in over 5oz. Green and pretty all the way through the harvest.
ya i have a friend who only changes to flush at the end of his cycle. But he doesnt use advanced nutes. Its the only chart i have seen that calls for a weekly res change. Not really trying to change six reses. weekly
I never use to change for the whole cycle when I ran hydro using GH nutrients. You should not need to change the rez when done correctly. Just top off as needed. But this means ALL your bases are covered and you grow a plant/s without any hiccups. It takes practice.
I think it depends on the size of your rez and the amount of plants on it. I think changing the rez periodically is wise, but as Chef said, if your grow is done without flaw then it can go without changing. The problem with doing this is that if you don't get precisely right then you may not see problems arrise but the yeild will suffer if there are unnoticed or unsolved issues. It also makes you succeptable to difficult PH problems that can have you "chasing yer tail".
I use 10gal totes with 2 plants in each tote and I change them every 2 weeks. I am considering modifying my setup to use a 15-20gal rez so that I don't have to change as often.
Plants do not uptake nutrients evenly. You could have an overabundance of some nutes in your res and deficiencies of others. When you top up, you will still have a condition of too much of some things and not enough of other things. While I do not believe that it you need to change every week, IMO, you should change out. I really like to changer mine out every 10-14 days.
I run dwc buckets and change out in about 14 days when in veg and the plants are small. In flower I change out every 7 days because like THG said they take up different amounts of nutes plus when in full flower there is not much left in the rez/buckets any way after 7 days.
I like the idea of putting them into clean buckets or totes as that eliminates any build-up of minerals that aren't used by the plants. In the grow-lab, we have 1 12gal rez for every 6 plants (2 plants per tote and 3 totes on a rez). When my partner gets lazy and doesn't change out the water for several weeks, what gets dumped out looks and smells like piss.
If your rez is 10-20gal then you don't have to change it every week. You could get away with every 2 weeks. If your rez is smaller than 10 gal then it is best to change it weekly. My partner uses 12gal rez and he found that having a pump in the rez to just move the water around vigorously helps to keep the nutrients well disolved and keeps the PH more stable.
That is what I use as well and I try to let it go for 2 weeks if it stays stable. If the PH gets jumping around too much or the ppm gets too high and the plants look like they aren't drinking, then I will go ahead and change it. If you have several plants(3+) pulling off that 1 rez then I would say change it weekly. I only have 2 plants on one 10gal rez.