Saltwater tanks require a lot of know-how to establish and maintain. You might want to decide what type of marine tank you will enjoy before you get started.
There is a certain mystique to the marine aquarium - the fish are generally more colorful and exotic. Reef and invertebrate environments seem very alien to land dwellers like ourselves.
Salt tanks have a reputation of being expensive to set-up, complicated to run, and more apt to fail. While marine tanks may be a difficult challenge for beginners, knowledge and common sense can overcome the difficulty of beginning in this new hobby. New marine enthusiasts would be well advised to read every saltwater aquarium book they can lay hands on and to study on saltwater related websites like reeftime.com. Another thing a new marine aquarist can do to help find success is to find a local mentor that you can go to for advice. Most areas have a local forums where you can ask questions and meet experienced marine fish keepers.
Here are the five main types of marine tanks to consider keeping, in order of difficulty and expense:
Simple Marine/Fish Only
The easiest saltwater tank - one populated mainly with different types of damselfish - is about as hard to care for as a freshwater cichlid tank, and only slightly more expensive to set up and run. You will need very good filtration, heaters, salt and salt hydrometers, a good book on basic saltwater tanks and a tank of at least 30-40 gallons for best results. Yes, you can get away with a smaller tank and much less fish - but a larger tank will lead to a more stable environment, helping you find success in the marine arena.
Damsel fish do cost more than most freshwater fishes (more than $5 a fish), but are much, much cheaper than almost any other saltwater fish. If you are going to be making mistakes with saltwater tanks, it's better to start off with these relatively inexpensive and hardy little damsels. Certain freshwater fish - notably the livebearers, can also be adapted for salt water. Either way, this is the best way for a budding marine aquarist to get a few notches on the old belt of experience.
This is not technically a marine tank - but it is not for freshwater fish, either. A brackish tank simulates an estuary environment - places where fresh and salt water mingle. Many lovely animals are adapted to this type of environment. Puffers, eels, archers, scats, monos and livebearers are often seen in such tanks. While brackish tanks have their own set of maintainance rules, these are often easier to care for (and are less expensive) than marine or reef tanks. It can be hard to find certain brackish species in local stores, however. Most brackish animals and plants can be ordered online at the very least. Mangrove swamp themes are popular and incorporate areas of both land and "sea".
Marine Fish Community with Live Rock - most of the desirable saltwater fishes fall into this category: clown fish, tangs, butterflys, cardinalfish, squirrelfish, wrasses, angels, triggers, dogfish, grammas. These tanks, once set up properly, can be quite self-sustaining - but only if very large tanks are used - 75 gallons is not too big. You will also need things like protein skimmers, powerheads, live sand and perhaps an attached refugium. Marine fish are very sensitive to fluctuations in salinity, temperature and water quality, so you will want to spend the money on proper tank electronics. The necessary equipment is somewhat expensive, and the fish are also pretty spendy. You don't want to make mistakes with a $50 fish - and that is a cheaper end of the marine fish price spectrum! Of course, you will need to do your research about which fish are peaceful in the tank with others, and plan your community accordingly.
This is just like a marine fish tank, but without the fish. In this set-up, the emphasis is on a community of cohabitable invertebrates. These creatures are fascinating and appear truly bizarre. Do your research, once again, before tossing shrimps, crabs and crazy-looking whatnots in your marine set-up.
These are those glorious, colorful, alien-looking tanks full of corals and anenomes. They may or may not actually contain fish, and if they do, are an afterthought. Special lighting equipment is needed, in addition to the usual marine tank necessities. These tanks require very, very specific care, and can cost thousands of dollars to establish and maintain. Fish must be chosen with care to be compatible with the living corals, and must be used sparingly. After all, fish add to the bioload, and can ruin the perfect water conditions demanded by reef aquaria. Gobies and blennies are common reef inhabitants - indeed, they need a reef environment to survive. Those of us here at reeftime.com to help people enter the reef keeping realm and to help people have continued success with this wonderful and fascinating hobby.