Land products contribute very little or nothing to the nutrition of the marine ornamental fish. Some products do put weight on the fish, but that isn't the same as being nutritious. Others create nitrogen wastes in the tank as they pass through, undigested, the intestinal tracks of the fish. But if the land products are far down the ingredients list (that is, they are one of the minor ingredients), I wouldn't worry about it.
The prepackaged foods that come to the US from Europe can't contain natural macro algae. There are restrictions to what marine lifeforms can be harvested/used in the fish food industry and macro algae aren't allowed. However the use of Spirulina and powdered kelp are very good for omnivores and herbivores. Because of this, they offer vegetable substitutes and then have to 'sell' the hobbyists that these are just as good as natural greens from the sea. Thus, rumors and myth-information are spread.
Gelled foods do provide the best chance to get the nutrition into the fish. This is explained in the fish food/nutrition post. Fish Health Through Proper Nutrition
For homemade foods, the subject has come up before: Home Made Fish Foods
The prepackaged foods that come to the US from Europe can't contain natural macro algae. There are restrictions to what marine lifeforms can be harvested/used in the fish food industry and macro algae aren't allowed. However the use of Spirulina and powdered kelp are very good for omnivores and herbivores. Because of this, they offer vegetable substitutes and then have to 'sell' the hobbyists that these are just as good as natural greens from the sea. Thus, rumors and myth-information are spread.
Gelled foods do provide the best chance to get the nutrition into the fish. This is explained in the fish food/nutrition post. Fish Health Through Proper Nutrition
For homemade foods, the subject has come up before: Home Made Fish Foods