DWC Adding nutes question

If I start at 500ppm with my general hydroponics gro,micro,bloom... And my plant is drinking it up to where I am now at about 400ppm... Should I let the PPM keep dropping until I do a res change? Do I add more nutes to keep the PPM the same/gradually increase it? And I'm using a 3 part nute solution... how do I know how much to put in of each solution... I'm a little stoned right now so I feel like I should know these answers but I'm drawing a blank...

I would bump your ppm up as they are taking much more nutes then water meaning they be "hungry". Set it a little higher and adjust the next day, I like to keep getting a little lower ppm so I see they are feeding and not rejecting nutes or burning by raising ppm in res. Typically 50ppm or less the next reading I keep, sometimes 50-100 as I am still trying to find what is a sweet spot.

I change my res every 3 weeks so I top off and adjust to my ppm I want to maintain. I have tried topping off with a 30% mixture in gallon jugs to help keep a proper mixture but really didn't see any change then adding nutes as I need them by reading ppm and adjusting.

I just topped my res yesterday and actually upped the PPM by about 150 and the plant is actually loving it so far... Amazing how much quicker plants grow in hydro rather than soil... I have tomato plants that sprouted from seeds 2-3 months ago in soil and they are half the size my damn MJ plant that is only 5 weeks old.

I never change my rez, Keep my rez between 450 an 750 during veg, 750 to 1300 during flower