I agree with UrbZ.
I grow in super soil and compost. I use 5 gal fiber pots, but have used 2 gal and graduated up to 3 gal black plastic landscape pots. They are pretty cheap at the big box stores in the garden dept. They have plenty of holes. I use a bottom layer of super soil, (kind soil), and then compost mixed with perlite to make sure drainage is adequate (about 80% soil to 20% perlite). Don't water until you lift the pot and it is light, or if you stick your finger to the first knuckle and feel no moisture. I have short fingers so I don't water until I can feel no moisture when I stick my finger all the way in the dirt. Or I can feel the bottom of the fiber pot and if it's dry, then it needs water. If you water to run off, don't let the pot sit in the run off, let it soak it up or dump the excess water if it sits around for a few hours. I think you are supposed to ph your run off water, but I don't water to run off so I am not used to doing this.
Have your bigger, new pots, soil and everything you need ready when you go to re-pot your plants, do what UrbZ said and cut off the rotten roots without damaging the good ones.
Try to use the best organic compost without any fertilizer in it, just worm casings and mix it with the perlite very well before adding it to the pot. I use a garbage bag to make sure that it's all mixed up evenly, put a layer in the bottom of the pot, put the plant in, and finish filling the pot with soil. Normally I will water slightly and let the soil settle and the next day go back and see if it needs more water. But that's just me. We all have our different ways to get the result we are looking for.
Good luck!