Proper nutrition is not an opinion. It has been studied to a great extent. It has consistently been shown that diet has a huge role in immunity, growth, and vitality. Specifically with probiotics and the proper fatty content. Most dry foods have no probiotics, this is beginning to change a little, but not much. The fatty content, however, is something that is not nearly enough in dry foods. the reason being if left on a shelf the food would go rancid quickly, so dry food producers take the oils out, and any fats that do remain are broken down enough so that they have very little real value. Look at the back of dry food. Whatever the percentages are after protein, fat, and fiber are completely useless filler. And it's these fillers that all get pooped back out by the fish, adding to PO4 and NO3, whereas frozen or fresh food has a higher content of useable food for energy and growth. Also, in what passes through the fish with the frozen or fresh is more readily taken up by corals, so there is less waste, less PO4 and NO3.
Fish can live on a diet completely of dry food, however the risk for disease goes up, life expectancy goes down, proper conditioning goes down(which also affects coloration and displays). Humans can live on a diet of just dry food too. Think of field rations. You can live quite awhile on them, but your life expectancy is not going to be that of someone eating a well rounded diet of fresh food. Fish's ability to survive on this diet is much more a testament to their durability than to the husbandry they are provided.
Frozen food should be only a treat once a week unless you have fish that will absolutely only will eat frozen.
Dry food should be what supplements the fresh or frozen. People get away with it, but again, dry is not what is best for the fish.
If your fish look fat and healthy then they are fine. A sunken head and stomach would be signs of under eating and then maybe frozen is needed to fatten them up but once a day or every other day.
Looks can be deceiving on this. Again, look at people. Most people that don't look skinny are actually far from healthy and diet has a lot to play with this. Eating too much junk food, fast food, or processed foods leads to high blood pressure, blood sugar problems, low energy, behavioral problems and death. Just because a fish is not emaciated is by no means an indicator of optimal health.
Feeding frozen all the time only leads to high phosphates and nitrates. If you don't mind 20% water changes once a week then feed away. Otherwise you will end up with very high levels and unhappy SPS and LPS.
Dry food has more waste in it than frozen, especially if the frozen gets quickly rinsed before being added to the tank. Where the biggest issues for waste arise is the quantity being fed. All too often, those feeding once a day, or more egregiously, once every other day, feed a larger size meal. By doing this a greater quantity of food is missed and is just left to break down in the tank. Even the food that is eaten has less value. Fish's digestive tracts aren't designed to extract nutrition from these larger meals, so it will pass through without the fish getting the full value of the food.
Whereas using the same quantity of food, but spreading it out over multiple feedings has less waste, as the fish are able to catch more of it, and they are able to digest that quantity with less waste through their digestive tract.
Corals are animals as well, and the single best food for them is fish poop, not ashy fish poop with undigestible filler, but fish poop with useable proteins intact, which in turn actually encourage coral growth.
Nutrient export is essential, though. If feeding properly makes keeping nutrient levels in check difficult, than it is more a case of stocking levels being too high. So instead of cutting down on the fish getting the feedings in a way that will best benefit them, why not cut down on the number of fish being kept. When you take a fish home you are becoming thei r caregiver, their steward. They don't have any other options available. They can't move on to better hunting grounds.
Again, the op's schedule was also in play. Feeding every other day. Just imagine for a minute if something happened to you(anyone still reading this), maybe an emergency came up and you had to go to the hospital for an extended time. If whoever was taking care of your kids(for sake of illustration) only fed them every other day and it was just ramen noodles when they did get fed. How would you feel about that? Or since fish aren"t even close to being as valuable as a person, they did that to your dog, only feeding every other day. This is more acceptable, but would you want it to live the rest of it's life this way? Fish may not be seemingly as valuable or as important as a child or a dog, but they are a living animal, they are a pet. They are not some piece of art to beautify a space in the house, They aren't some recreational activity that can be forgotten about when you lose interest.
