When I did dwc in separate bubblers, I changed the res every 2 weeks. Which was probably not often enough. I'd top up with tap water every other day. For the res change, I'd mix up the nutes in a spare tub, carry that down the ladder into the cellar, lift up a lid/plant and put it on the new res. Then I'd carry the old res up the ladder. With 8 plants, it was an exhausting day.
I have done a full grow without a res change. It needs RO water, auto top up, the lucas formula and a BIG reservoir. The only maintenance is reading the ec once a week and adding back enough Micro and Bloom to get back to full strength. I'd no sooner finished that grow when the housing told me that workies would be in to fit a new kitchen and they needed cellar access. Good fun getting rid of 700 litres in a hurry.
During that shutdown, hempy was posting about his buckets so next grow, I gave it a try. It suited me better than dwc so I've stayed with passive hydro since. If short on space, the efficiency of dwc is a factor. If there is enough growing space to stay self sufficient whichever system is used, then might as well do whatever is most convenient.
I haven't done this but I've read of dwc growers that do partial res changes. afaik, it's common practice with aquarium guys. The grower I first read of did 10% a week. Which may or may not be enough for you. If you want to try it, I'd play safe at first and start with 50%. If no problems, then try 40% etc. The problem with trial and error is that at some point in time, there has to be an error.
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