I use mussles for years. I cook them, then freeze. I cut thin slivers, mix it with finely cut frozen peas. Put it in water,stirr and discard the very fine 'dust' and then feed it a bit at a time so it doesn't sink to the bottom. The fine stuff is good for the smaller fish and young ones, the bigger pieces are snapped up by the bigger fish. When they get less keen, I stop.
I have malawi tank!