roots will reach the bottom in a few days, but that's not the same as rooting out the pot, you will know when they are rooted out when you have to water once a day, when in flower you will be feeding at least twice a day. Remember coco is hydro, do not treat it like soil, if you do it will be no better than soil. Yes you feed with every watering and water till you get run off about 20% and you won't get excess build up of salts. Coco plants should thrive but only if you follow what i have said, any experienced coco grower will tell you the same.
Feed strength should be a third of what the nutrient company says. You really should have a Ec meter and ph meter. My coco grows in veg never go above EC1.4 and in full flower normally EC1.5 pH 5.8 in veg and ph6.0 in flower. My tap water is EC 0.4 so i top that up u til it says 1.3 etc.
Hope i have explained that enough for you.