You can only add so much at one time - PH spike.
Reactor is easy to build, but may cost a few $ in the end to set up (two pumps, one possibly a quality peristaltic pump which could cost a few hundred $'s, and two digital timers $40 plus making a reactor $50-300).
You can add manually daily, best done after when the lights go out, but that can become labor intensive over time (how many days per month will you miss dosing because you went out or something?).
Personally, after trying numerous approaches, I'm now running a DIY reactor on a continuious slow drip all day with a seperate RO top off.
If you just add the powder to the system water, you will get at least some precipitate - not the desired effect. It's meant to be mixed with freshwater then slow dosed to the tank.