I've had a hangup for a long time about having a very aerated medium...mostly from seeing the results of soil compaction, and low quality, high clay soils...after playing with different ratios of coco, or perlie/vermiculite, I came to the conclusion that- yes drainage and oxygen to the roots is important, but too much is a waste of bucket space, and weak. my new guideline is: no more than 25% filler.