PPM question

I am doing my first DWC hydro grow and after one week, my PPM lowered from 350 to 325. Does that mean that my plants only needed 25 PPM for that week? So next week I could give only 25 PPM to.plant during res change?

Ok um ill give u general info and then ill make an educated assumption. 1st dwcs are very simple to set up but they have a few cons. If u aren't using the all black food grade buckets then you need to wrap them in 10mils worth of black plastic to black out the buckets. A lot of dwc problems happen here because bacteria in the water multiply and change the ph.
2. Incorporate a reservoir. It makes cleaning and making changes a lot easier. If shit hit the fan in a dwc u gotta operate with the plant in the system and hurry and finish before the roots dry. With a res u can just operate on the res. As for your question its kinda weird to me for your ppms to be that low and your plant not be deficient. Its not impossible but kinda weird. This what you do. Take a pic of the plants. Your set up. Wats your water level, ph ,temps, and take a root pic. And how are you getting the ppm numbers? But generally though once you find a given strains sweet spot you'll know because it'll start drinking more.

No. Your plants would of also drank a lot of water. My res usually goes up in ppm. I'd suggest going stronger rather than weaker. I work in EC and not sure of my ppm in my dwc but it's a lot stronger.

How old are your plants?

Generally:
EC goes up; PH goes down quickly=over fed
EC goes up or stays stable; PH goes down slowly or stays stable=still slightly over fed
EC goes down or stays stable; PH goes up slowly or stays stable= close to perfect
EC goes down, PH goes up fast= under fed

Ideally, you want your EC to stay stable or drop slightly while your PH goes up slowly over a few days.