I know it's somewhat intimidating when you look at the fish food aisle at the pet stores, but like food designed for human consumption there's a difference.
I have been doing this for some time and I've spent hundreds of hours with regards to fish nutrition as I truly believe it's one of the major reasons behind the deaths of fish. Followed by overfeeding, now when you combine the two it's a recipe for disaster. Read the labels when looking at the products, don't judge based on what size magazine ad they have or what your local pet store is using...use what's best for your fish. Here is a good read about fish nutrition from Pablo Tepoot the developer of New Life International.
New Life International Inc- Fish Food, Books, Aquaculture and more! - Basic Fish Nutrition
I have been using this product with excellent results for nearly eight years now, previously I think that I tried every different brand of food but still I kept searching for the most complete one food that does everything and this is it.
I personally would not feed my fish anything that contained MSG(added for taste) or astaxanthin(preservative). Plus if you read the ingredients you'll see lots of low quality binding agents and corn fillers. The other issue I have with Hikari and most other fish foods is they use the leftover parts that the other industries don't use rather than the entire fish, so there is more waste which is evident from the ash content. Fish can assimilate only so much mineral content, and any excess will simply be adding unwanted pollution to the aquarium water.
The last big and most important issue I have is about protein it's not the percentage, it's the quality of them proteins themselves. Food that derives it's protein from high soybean, corn, wheat flour and other fillers is not nearly as digestible as a high quality pellet that uses quality ingredients. Proteins are made of amino acids which contain nitrogen, carbon, hydrogen, and oxygen, so as the fish is breaking these poor quality foods down they in turn make a lot more nitrogenous waste which as everyone knows will effect water quality.
Spend some time looking at what's best for your fish, in the long run you'll find a much higher level of success.