avoid stem rot rockwool

[plzhelp]

I am designing an nft system using rockwool cubes that fit into holes in a pbc pipe angled slightly with the end of the pipe pouring into the reservoir with a pump

ive seen so many videos of people getting stem rot using rockwool

how do I avoid this?

I may or may not use a timer to turn flow on and off

I don't know the ideal time intervals of flow on and flow off if I were to use a timer

I am very worried about getting stem rot even while I am developing the root system before I place the rockwool with plant into the pbc pipe

maybe I can avoid stem rot by having only the roots dangling out of the rockwool in the nutrient stream, instead of having the rockwool touching the stream like I originally planned. but this would require development of a very good root system before placing the plant in the pbc pipe, increasing the chances of getting stem rot at this point

any tips would be greatly appreciated
tyvm