Hello,

Lets pretend that one ounce of your 15-30-30 NPK, added to one gallon of water, breaks down like this. 50ppm N - 100ppm P - 100ppm K...

...Now if you were to only give half of the amount (.5 ounces) then you would end up with a concentration of 25ppm N - 50ppm P - 50ppm K...

...So no, Adding at 1/2 strength will not work just as well as a full strength feeding.

I hope this helps

Peace