All-in-one (AIO) nano aquariums can make for great fish only or reef tanks, provided they get a little boost from equipment add-ons and modifications. Usually, the lighting on these aquariums is insufficient to house corals long term. Most of the nano tanks come with power compact fluorescent lighting, which is perfectly fine for fish only tanks, but corals need a little more juice from sources like metal halides, LEDs or T5HO. So, hobbyists usually pull the stock hood and replace it with some aftermarket light fixture. On the filtration side, the typical AIO comes with a few chambers behind a false wall, which serve to hold media like carbon and some form of bio-ball. These too are usually inadequate for a healthy reef system. To fix the filtration issues, most hobbyists add a small protein skimmer, hang-on refugium, or some other form of external filtration. With each of these add-ons, the aquarium becomes that much more effective at processing fish and coral waste, allowing for a healthier aquarium and more stable water parameters.