my diy food makes a tiny bit of a mess but not like that. i think your problem with it is that the piece was too big. if you cut into bite sized pieces the fish won't have to chew it up so much. when i feed my 5" piranha, the pieces are around 1/4" by 1/4" cubes. they can be eaten with very little mess due to the size. you could also add a little bit more gelatin to maintain structural integrity, but food size is a big part of clean diy food.
what was your mix specifically? i agree with your earlier post to add something they already recognize. my food was 1/3 pellet (which my piranha didn't really prefer) and 2/3 fish fillet that he takes instantly. garlic was also added cause i've read that it's a food attractant for fish, and is good for immune system. i wouldn't add flour in a gel diet as it's basically an unnecessary binding agent, the gelatin should be enough. you see flour being added when making diy dry pellets.
my recipe was
1/3 ground Tetracichlid jumbo carnivore sticks
2/3 fish (walleye cheek, tilapia fillet, salmon cheek)
1 clove of garlic
1 tsp paprika (comtains lutein and beta-carotene, good for yellow and orange color)
~2 tbsp unflavored gelatin
enough water to make a thick pudding like consistency (for me it was a round a tablespoon maybe)
