Personally, I find it hard to blame this on the fert. Fish emulsion is pretty low concentration, and organic so not likely to be the problem. Half strength miracle grow would also be pretty low concentration. Given that there are other bonsaists using fert at 5X the recommended strength, without problems, its hard to imagine that 1/2 strength would be problematic.
So I don't know what the problem is, but IMHO, its not the fert.
- bob