I think your koi/goldfish hybrids could be hindering the recruitment of your fish. Having 10+ koi/goldfish are probably making your water cloudy and allowing too much suspended sediment to settle on developing fish eggs and reducing hatching success. What is the average measured water clarity with a homemade Secchi disk or similar white object? Another problem could be the koi/goldfish could be eating freshly hatched larvae while they lie on underwater surfaces before swim up.
I have a couple ways to make smaller food sizes for the minnows/shiners. Add just enough water for several hours to make the pellets softer and easy to grind. Then feed the moist ground food in 1-2 days or freeze it then use it in small batches. The other way I do it is air dry the moist food and store it as dry food for up to several months.
