Don't worry about the flakes, they'll fall eventually and get eaten. I put two shrimp pellets in daily, but rarely see them getting eaten. The kuhlis like to hide most of the day.
One of mine is no longer a bottom dweller. My wisteria rotted at the base of the stem over a year ago and has been a floating plant since. I changed jobs a month ago and had to move the tank, which was traumatic for everyone. Now, one of the kuhlis lives in that floating plant. Sometimes you can see him slithering through. One of the others will sometimes come to visit, but the third never comes out of the little jar decoration he lives in.
They'll grub around on the bottom for food, and eat about anything. You may not see them eat often though, because they're just plain shy.