Few questions on radiator tube size

Ok guys well i suppose its time, ran her on sunday and of course the classic industries radiator appears to be leaking at the bottom tank on the drivers side. Not dripping but enough to notice, guess its time to go aluminum. I contacted wizard cooling and they recommended to go with the 1.25” tubes over the 1” they told me anything at or over 400 hp they recommend the 1.25” tubes.

i have been using 50/50 conventional green coolant and they also recommended i use a corrosion inhibitor as well. Do i need to? Has anyone used a corrosion inhibitor?