how often you guys change water in dwc?

Hello Grz! The answer to this question varies greatly depending some basic DWC specifics and since I am unfamiliar with the nutrient line you use I will share explanation. Let me start by saying this *generally swap out to fresh 1-2x per week.* Now some things to think about... Personally I try to do entire runs with 0 swaps. For example my current DWC is over 50 days in with 0 swaps and I intend on going all the way! Here are the reasons I attribute to why: I use a "sterile" dwc solution / nutrient line which typically requires the least amount of swap out's. I pump much more oxygen (but not too much, have done that before also) then usually needed per bucket. My buckets stay cold to very cold - this is very important factor. Also I do not use "cleaner" enzyme products such as hydro-guard to neutralize the bad bacterias (ie root rot) because generally speaking I have little to no bacteria*** and when I the past I was concerned I used H2O2. Now on the other end is "Bio-ponics". Using "all natural" raw and often living ingredient nutrients. This in theory is great but I've rarely seen it very successfully employed. It requires much attention, knowledge, and the most swap outs in DWC setting. Finally I'd say 80-90% of nutrient lines fall into the middle category between the "bio" and the "sterile". Most nutrient lines used in DWC utilitize both natural (ie living beneficial bacterias and the sugars to feed them) and unnatural processed (ie "PGR"s) ingredients and therefore requires the second most swap out's: though this can still vary greatly depending on specific nutrient line. *** This is because of having a high ORP measurement in "sterile" solution. "The Power of ORP Many of you may have heard of the term “killing power” before. This is a slang term used to define ORP. The killing power refers to a solution’s ability to, in essence, kill the micro-organisms inside that solution, causing a higher mV reading and an increased ORP. Solutions that maintain a high ORP are considered to have high killing powers, which translates to a sterile environment. Drinking water, for example, should have a high ORP to reduce potential contaminants that can be detrimental to human health. Another common reference to ORP that circulates in the industry, is how “dead” or “alive” your water is. Don’t let the verbiage in this reference scare you, however. Dead water is considered sterile and free of disease, with a low- to non-existent concentration of bacteria." --https://www.maximumyield.com/the-power-of-orp-how-to-get-the-most-out-of-oxidation-reduction-potentials-in-your-hydroponic-system/2/1316