I feed them 4 days in week, other days I feed only Satanoperca with pellets. Crenicichlas are hunters, they are carnivorous. I have no plans to feed them with vegetable foods or learning them to eat dried food. Luckily mine zebrina eat chopped small fish without any problems. I plan to buy them frozen mussel meat and frozen shrimps in hypermarket.
I have big external biological filter. It is made from 20 gallon tank and inside is 10 gallon of filtration materials (8 gallons of polyurethane foam and 2 gallons of Eheim substrat pro). And small internal mechanical filter to clean dirt Satanoperca make during sifting. I change 50% of water weekly and I have a lot of floating plants. I had no problems with water quality so far.