I have leaf litter on the bare bottom of the breeding tank that I leave there to grow food.
Moss also harbors snacks for the fry.
I throw in a small amount infusoria a few days before starting the breeding schedule. I tend to include a little piece of mushy veg to give the culture a solid amount of bacteria to feed on and multiply quickly for the fry.
For dry foods, I collect the fish feed dust out of each container as I finish it. The dust from all the different brands and types go into a mixed container. I sprinkle this dust in fry tanks. Has worked well for me with guppies, danios, tetras and hillstream loaches.