Mixing Nutes

I'm a little confused what additives to count ppm and what doesn't. For example, if my plant is using 500 ppm in bloom... I might have 150 tap water and 75 silica and 500 bloom for 725ppm solution.

Next I decide I want to add 80ppm hydroplex as a bloom booster. I want to keep feeding 500 nutes... do I add the hydroplex on top of the bloom nutes for 805ppm solution, or run 420 bloom 80 hydroplex to keep the same 725ppm?

Add it right on top. I would keep it around 1000ppm until you figure out how much YOUR plant needs. It might be fine with more, or it might perform the same with less. Check pH daily, check ppm every few days. Good to go. Hope that helps.