These are always tricky to figure out. As has been said many time, it's easy to over fertilize, hard to under fertilize. Same goes for water to some extent. I think the watering thing has to do with essentially water-logging the roots such that nutrient absorption is inhibited. Thus, it's could be an iron deficiency say, but because of a root issue (whether from burn of fertilizer or the over-watering issue).
For years we've raised (I know, I said raised) orchids. A common problem early on was the leaves turing yellow, leaf drop, leaves getting "wilty", and ultimately death. Thinking intuitively, it would seem that they weren't getting enough water, or fertilizer. When you'd take the dead plant out of it's pot, the roots were essentially mushy / rotten. It turned out that it was OVER watering. Quickest way to kill one of those babies. I've seen it with tomatoes, and other plants, and I'm convinced it's the easiest thing to over do.
Early on the small plants don't need as much water. They just don't have the root system to handle it all, and they don't have the leaf system to need much either. When they get bigger, you'll have a huge leaf burden, and the water loss will be exacerbated by the shear volume of plant material using water to go about it's various required photo-reactions. That and it'll be warmer. So, you'll need more water then, and it'll be harder to over water. But early on, it's real easy...even if it seems to drain well.
As for fertilizer, I've only done it once so far on my new hop plants, and it was at 1/4 strength.
All the best,
Mike