In my opinion, fish food does make a difference. Best way to put it, If you feed a kid McD's chicken nuggets his whole life what is this kid going to turn out looking like.. Ok, I'm not going there but anyway..LOL Good food is nutrition, There are some companies that use 50% filler in their food and the other 50% is well junk. This causes the fish not to be able to digest correctly therefore clouding the water when they poop. Some companies use HIGH protein food, rich with fish oils. Great if you want to grow fish fast, But feeding this type of food requires EXCELLENT filtration, Not the run of the mil filtration but yes, the high end stuff! This food is designed for growing fish large and fast, it's designed to get the max out of color before a show. The fish are fed heavily to bulk them up, this means that not only does the fish poop a lot from being fed heavily but they also have all these oils and extra proteins that produce large amounts of DOC's. these foods have a very short shelf life span, They can actually spoil and go bad if not stored correctly or aren't used soon enough.
In a water garden these two extremes need to be avoided. Sadly the first food is there InMyOpinion to help boost the sells of chlorine neutralizer, water clarifier, algae away products, etc etc. See where I'm coming from. cheap food = addition sells
High quality food has it's design but it's more specific and is always way more expensive, Therefor more people avoid using it as it's not the most readily available any way.
So now your to what to use. Finding a good name food isn't hard, what your looking for is variety, variety as in a winter food, (wheat germ) summer food, low filler food usually will have color enhancing additives, and spring and fall food, these are easier to digest foods that do have fillers, they are there to help fatten up the fish prior to or coming out of winter dormancy.
Fish are like humans, feed them the same thing all the time and that's what they think food should be, Don't feed every day, make them do what comes natural and hunt for food. feed them variety, a little pellet today, some freeze dried krill tomorrow, maybe a few broken up honey nut cheerios for a treat. even some fresh veggies with seeds removed, yes they like i! but if the haven't been introduced to it they will be slow realising that it's food. take the time to watch and remove anything not eaten within about ten minutes. But also give them breaks. If your going away for the weekend, leave them be, have someone come check on them and the pond and give you a update but HIDE THE FOOD! Overfeeding is dangerous, for the fish for the pond and for your sanity. lol Always remove uneaten food before walking away from the pond, But your fish are your kids, want vibrant colors and healthy fish, feed variety, don't over feed and allow you fish to hunt for some of their food naturally.