Google it. You'll find tonnes.
Really, DIY fish food is anything that you think is best to feed your fish so pick and mix any and more: mild paprika, frozen shrimp, white fish meat, spirulina, eggs, beef heart, earthworms (clean), blanched/cooked greens (spinach, green peas, water spinach etc.) etc.
What I am currently using:
- banana (with peel!)
- chicken liver (it's oily so it's not recommended unless you have a really good filter)
- white fish meat
- water spinach
- gelatin (to hold things together)
1) Blender each ingredient separately (except gelatin)
2) In a saucepan - add and cook (throughly) the meats first
2) Add in the pureed fruits and/or greens and gelatin last then cook it for about another one or two minutes.
3) Pour it on a large tray - make it at least 0.5cm thick. Let it cool/solidify then freeze it.
When it is frozen you can cut small cubes and feed it to the fish. All my fish (Angels, Guppies, Betta and Corys) go crazy with the food I prepared for them. The only downside is that it sinks to the bottom. I don't know how to make it float. Plus the oil.. but I have emerged plants (pothos, philodendron and peace lily) above the aquarium to filter that. And you can always replace the chicken liver with something else like frozen shrimp.
Don't use onions, garlic and salt. We're not making food for humans haha.