Nearly every aquarium fish has a unique place in our aquariums whether it be the ecotype they fill, their personality, or those bright colors that just draw in everyone's eyes. However some marine fish are more than just a pretty face, some of these select few can play a crucial role in keeping our reefs has a functioning ecosystem.
Damsel
Often damsels are often seen as the go to fish when it comes to starting up and cycling a new aquarium due to their cheap price, variety of bright color, and resilience to mistakes or poor water quality. Down the road this usually turns into that one fish that just won't die and seems to want to kill everyone else in the tank. Now despite this their benefits still outweigh the problems that come along with them. Damsels are known for eating various small pest that may harm corals such as flat worms. Now not all damsels are made equal, members of the genus Chrysiptera tend to be on the smaller side and generally better at eating pests along with being not quite as territorial as others, the springeri damsel specifically tends to be a great candidate. Damsels such as the domino, jewel or velvet are on the larger side and thus much more aggressive and best suited for predatory tanks.
Mandarin Dragonet
Mandarin dargonets are often the poster child for anything reef related, and for good reason. When it comes to pure appearance not many fish can top the mandarin dragonet. Nearly everyone in this hobby, beginners and experts alike, either want one or already have one, unless they don't know exist or can't keep up with the diet requirements. Dragonet has a whole only eat microorganisms such as copepods, to keep them in an aquarium you must have enough surface area for them to breed faster than the dragonet eats them. In an established aquarium this actually works out well because you don't have to worry about feeding them. And now with captive bred individuals becoming more and more available, who will eat prepared foods, this amazing specimen is seeming to be a better choice for every aquarist. Aside from those colors what makes dragonets such great additions to a reef tank is that they send all day forging for small critters like the previously mentioned copepod but also various coral pests.
Wrasses
Saying wrasses are on the list of 'some of the best hard working marine fish' is very broad as their are roughly 500 species of wrasse. Now many of these aren't found in the aquarium hobby, but there is still a huge selection if them to choose from. They verity greatly in color, size, and rarity so there's always a good choice for everyone. Liked to two groups mentioned before wrasses main purpose is for pest control. The main difference between wrasses and the others is that wrasses are much more efficient at pest control and due to the large array of species also good at controlling a large array of pests. Now some larger species like the dragon, hardwicke or the slippery dick wrasse, tend to be on the aggressive side and not always reef safe. Members of the Halichoeres, Macropharyngodon, Pseudocheilinops, and Wetmorella genus are good choices for some nice color, smaller size, and pest control. Of these the six line wrasse of the Pseudocheilinops genus is probably the one most people think of when it comes to wrasse pest control, While an argument can be made they are the best wrasse for the job, they can be a bit aggressive towards others, the pink streak wrasse is a good substitute for them and with a max size of only 2.5 inches is great for smaller aquariums. Other groups like the Cirrhilabrus (the fairy wrasses) and the Paracheilinus (the flasher wrasses) are famous for having some of the brightest and unique body shape but aren't quite as good for our purposes here, still amazing additions to any tank however.
Tangs
Often times when people are first getting into saltwater for the first time we recommend going for at least a 120 gallon if it's within the budget. Main reason is that water parameters are more stable and people run out of space faster than they think they will. However the second reason behind this is that this gives a large enough tank to keep a variety of tang species. This is so important because tangs are the ultimate algae eaters, whatever nuisance algae pops up, there is tang species out there that will eat it. Now granted there are plenty of other creatures that eat a wide type of algae, but the importance of a fish that can graze the entire tank in a matter of hours vs days can not be over stated. Sure emerald crabs will eat your hair or bubble algae problems, but it's very limiting how much a single crab can eat, and how fast they can get threw an entire tank. Then run into the issue that they can never get the jump on the algae if they eat it as fast as it grows, so often times you need a boatload of them to get the job done, and once the job is done, most of them will probably die off. All of these problems are avoided with some tangs, they get the job done, and get it done fast. Best part is that they make amazing show piece fish, with insane looking ones like the famous gem tang, or achilles tang. Or if you want something no one else has there are tons of hybrids and variants like the koi scopas. Of the tangs there are 9 main genus in the hobby. The Acanthurus which include members like the powder blue and convict are good for grazing on standard green or brown algae. Ctenochaetus or bristle tooth tangs are great because most only get six inches which is perfect for those with smaller systems. There mouth as you might guess is full of bristle like teeth which is perfect for ripping almost any algae of the rocks. The genus Naso is quite the opposite in size with some like the unicorn getting up to two feet in length. Obviously this means they aren't a great choice for most but they are some of the best for bubble algae should it arise. The Paracanthurus while it does include Dory, they also are almost completely useless for algae and bit more aggressive than most tangs. And lastly but arguably the most common is the Zebrasoma. They will often do good work on hair algae, green or brown, and work great in schools.
Foxface
Nearly everything mentioned about tangs is true of the foxface, with the addition of a few venomous spines. Despite this reports of being stung are extremely rare and the venom is fairly weak. Foxface are essentially like a tang in the algae eating ability and amazing show piece fish. The foxface is generally less picking than tangs when it comes to what types of algae they want to eat, especially hair, and bubble. There main down fall is that they can be a little shy at first and some report that they nip at zoanthids. This tends to be more of a problem with members like the gold spotted rabbitfish, decorated rabbitfish, or magnificent foxface, the foxface Lo (Siganus vulpinus) tends to leave them alone.
Copperband Butterfly
Finally, the best for last, or at least the most underrated. Copperband butterfly often gets a bad rep or is over looked for it difficulty of care. And while yes, it is without a doubt the most challenging fish on this list, there difficulty is often blown out of proportion. The main challenge with this fish is that they will refuse to eat, but as this hobby advances, collectors are using better practices and hobbyist are learning more information, and copperbands are becoming a much less daunting task. It's important to get a grasp for the fish and how they live. Copperband butteryfly fish have a long snout to reach into cervices and grab worms and clams as there main diet. So it should it come as no surprise they don't always take to normal prepared foods right away and may need some supplemental blood or black worms. They should also only be added to large systems that are fairly established. So why is this fish worth all that hassle. Copperband butterfly are the kings of pest control, it's very hard to think of a coral pest that they won't eat. They are also one of the few reef safe fish that will eat bristle worms and aiptasia. The main downside to copperbands is that due to that worm eating nature and feather dusters or coco worms will be toast, they also will eat small clams, however large specimens are safe.