We're not saying that Tetramin is going to kill your fish, but let's talk about fish food
.
The first 12 ingredients in Tetramin tropical flakes are
Fish meal, dried yeast, ground brown rice, shrimp meal, wheat gluten, feeding oat meal, fish oil, potato protein, dehulled soybean meal, soybean oil, algae meal
The first 12 ingredients in Omega One tropical flakes are
Whole Salmon, Halibut, Black Cod, Whole Herring , Whole Shrimp, Whole Krill, Wheat Flour, Wheat Gluten, Fresh Kelp, Lecithin
Omega one uses not one, but several fresh fish. Not fish meal like Tetra, fresh fish. 4 kinds. After that they use whole shrimp and whole krill (shrimp like crustaceans). There is no grain (binder) until 7 ingredients down the line. In the Tetra food, meanwhile, there is grain (rice) as the third ingredient.
Also, note that Tetra, instead of adding lots of natural protein sources like Omega One, adds several inferior, cheap protein sources. Dried Yeast, wheat gluten. Cheap cheap filler proteins. They even use potato protein for crying out loud. Have you ever heard of a fish eating a potato?
Feed your fish quality if you want extra healthy, beautiful fish with good color.
Omega Sea/Omega One
Ocean Nutrition
OSI
New Life Spectrum
Dainichi
Northfin
These companies all make superior grade fish food.
Pellets are always better than flake as they have a smaller surface area for things to oxidize in them. More concentrated nutrition as well. Your danios can probably take 1mm pellets if they are near adult size.
If you can't find quality foods at your local pet stores, order it online. Amazon has them all. So does Ebay. Or you can order from a specialized online aquaria retailer.
Get a 1/2 pound bag, take a little bit out at a time to keep in a little jar, and store the bulk of it in a sealed bag in the freezer.