Micropellets for a 4" fish? Try 1mm pellets. As for it gunking up in your filter, I'm still very much convinced that your FH is not eating all of it, but rather expelling it from his gills. I fed a tank full of FH fry 1mm pellets(The fry ranged from 2"-3"), didn't have any build up from the food at all in my filters. As for Hikari being harder than NLS pellets? I don't think so lol. I crush the Hikari pellets(The really big ones, I forget the size but much bigger than 3mm) in my fingers with ease.. I have to use a pestle and mortar to break down NLS pellets..
Crush with ease eh? what are you?? the Hulk? If it's that soft you might want to start keeping your food in containers.
