I heavily use pine bark fines and have no problems with gnats or nematodes. I am trying to solve some nematodes problems with plants purchased, but with root pruning and repotting I think I am getting to the success stage. Now I am different than most members when rooting cuttings. I root all cuttings outside in one gallon nursery pots, all year long and I think the pine bark fines has helped a lot. Now, I am very interested in trying coco coir, this will be the next venture on my list. I do not feel that you will get a 100% agreement on what mix is best, all I can say is what works best for me.