Aquariums are supposed to simulate a lake, river, or ocean environment (except, of course, for some). Pretty generally, how well your fish end up doing depends on how closely their artificial environment mimics natural conditions. This, of course, also applies to what you feed them.
Obviously, different fish species have different nutritional requirements; the most basic difference being that between herbivores and carnivores. The sad truth is that even specially-formulated flakes and pellets often fall short of providing the nourishment your finned friends need.
Commercially manufactured aquarium food is usually based on fish meal (all the parts of fish that humans can’t eat, dried and ground up) and spirulina algae. Grain flour (soy, wheat, oats, etc.) is used as a cheap “filler” to provide bulk and calories, and finally some vitamins, antioxidants, and preservatives are also added.
Even with pet food companies’ best efforts, there’s just no way that this kind of mixture can accurately replicate a fish’s natural diet. Many responsible aquarium owners therefore feed their fish supplementary meals for variety and to balance things out – freeze-dried insects, shrimp, and dehydrated seaweed all being examples.
The latter is an excellent way of keeping herbivorous and omnivorous fish alive, healthy, and happy. If you notice your fish becoming sluggish or aggressive, or behaving oddly in some other way, a poor diet might well be the actual root cause. You can use either nori intended for human-edible sushi or dried sheets made especially for fish, but how do you actually introduce these to your tank?
Simply tossing one into the water, either whole or shredded, will mean much of it isn’t eaten and instead just ends up fouling the water or getting sucked into the filter (and seaweed isn’t cheap). The more usual approach is to hang strips from a clip or hook, but this leads to much the same problem, especially if your fish are large enough to tear off pieces.
This product, by contrast, holds the seaweed in place behind a grille through which even larger fish can feed. They obviously can’t reach the parts of the sheet behind the lattice, but removing the feeder and manually shifting the seaweed around takes care of this problem.
Though it’s a great idea, there’s a lot of room for improvement in this design. It attaches to the side magnetically, even through ½” thick glass, but the magnets aren’t properly sealed so they may well end up rusting and putting unwanted minerals into your water. Also, the dispenser doesn’t float, so your fish can’t feed from the bottom. And if you drop it, you’ll probably get your hands wet fishing it out. Depending on the thickness of your seaweed, you might also find that the latch on the door doesn’t stay closed.
All in all, giving your fish access to algae is a pretty good idea, and this feeder is certainly better than a simple clip. The build quality just isn’t really reflective of the price, but I guess that’s sometimes just the case with innovative products.