To answer your question if you half dose you will need to reduce your lighting (easiest is to raise the fixture by a few inches) then you could do 25-30%, it also depends on the amount of plants you have as well.
Did you look over the Fluidsensor range.
If you want the control i think you do,it may be better for you to dry dose as you can adjust individual chemical amounts.
fluidsensor sell the chemicals individually and also have the small dosing spoons.
from what i can see they supply the others with chemicals.
if you want dosing levels let me know and i can try help you out.
i do understand it is a lot to get to grips with but it is not very hard just take a little research (as there are a lot of conflicting bits of info).
if you dry dose you can tailor it to you needs better than the premixed options.
but as i mentioned the main thing is consistency in the dosing (it takes time to see the changes)
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