DWC no water uptake, but nute uptake??

I'm growing in DWC, have a bunch of bins going. Some of the bins are way down in their water level, yet some of them after 3 weeks since the last water change the water level hasn't varied at ALL, it's pretty well right where I already filled it to. That said, based on a recent test my EC meter appears to suggest the ppm is going down, which would mean the plant is using the nutrients but not the water. I'm 3 weeks into flowering, would someone please let me know if I should be worried and if so what I should do about it?

The plant would have to use "some water".. lol.. and I wouldn't be worried about it not taking in a lot of h2o. Maybe the other strain is more of a "drinker".
All strains vary though, gotta keep that in mind. What 1 strain would like, maybe the other wouldn't. That's the "only" thing bout running my DWC setup I don't like! Can't run multi strains in there! Well, I guess you could, and I'm sure its been done. Just "I" wouldn't do it. Cause all strains are dif, one could "overdose" on nutes, and the other "eat um up".. lol

I feel you, but it's all the same strain, but that said they're not regulated, there's at least two different phenotypes at work, so I suppose that could explain. Interestingly though, I was looking for the ppm "sweet spot" and now ppm's are going up in almost all my bins, even the ones with little to no water uptake! I'll have to make another thread for that, can't figure that one out....