Green color hydroponics fish grow bed with standing for greenhousr aquaponic systems 2020*1030*350 description rotational molding hydroponics fish grow bed ,rectangular shape , lldpe material , uv resistant ,. The first thing you need to build a backyard aquaponics garden is a fish tank. i would not get anything smaller than 70 gallons if possible. if you have the option, get bigger. i went with a 100 gallon feed tank with a bottom drain. this will let you raise between 5-10 lbs of fish with an adequate sized grow bed. grow bed. the next thing you need is a grow bed. it is important to get a grow bed that is atleast 12″ deep when building an aquaponics system..