Do you have holes at the bottom to let full grown larvae out? Do you plan on mounting this over the pond?
Some sort of maggot platform mounted over the water is in my future pond plans. I've always thought of using fat and hide picked up from a butcher shop and letting the blowflies do their thing. The survival of the larvae into adulthood in my plan would be zero. However if you want to keep a population of only BSF going you may need to allow some to reach adulthood to provide future breeders. Maybe one bucket over the pond to provide fish food and another over ground to provide breeders would work. Keep up the good work I am very interested in how this turns out.
