The simplest of marine aquarium set-up types, 'Fish Only' or FO is a great place for a beginning aquarist to start, rather than jumping straight into more involved types of animals, demands/constraints and the added gear it takes to house invertebrates like corals and shrimp. This being stated, there is no reason not to pick up and use gear for more 'reef' oriented rigs from the get-go'¦ as these are indeed better in terms of providing a good environment and protecting your livestock from environmental harm due to fluctuating environment.

Here's a handy checklist of a 'stock' set of gear you'll want to have a successful FO set-up.

Tank: Like your bank balance this can't be too big. The larger the better by far, for providing room, dilution of wastes, space for your fish to get away, avoid each other in case of aggression (very common). What's more the more water you have, the easier the system will be to maintain. I strongly encourage you to purchase as large a tank as your space and budget will allow.

            Glass or acrylic, 'show' (tall and narrow) or more 'standard' (squat/low), the choice is up to you.

Stand/Support: Give careful thought to what your tank will set upon. When filled with water, gravel and more it will likely weigh a bit more than ten pounds per gallon! Your support needs to be chemically inert (so it won't rot/rust), strong (obviously), level and planar. Even if purchasing a commercially made stand, it's a very good idea to check its level on your floor (and possibly spread out the weight by putting a piece of ply under the feet if on a wooden one), shimming this up to level if necessary, and then again with the tank in place before it is filled.

Filters/Filtration: There are quite a few variations in gear and what they can/do here. You can 'get by' on an undergravel filter (for biological and mechanical filtration) and a protein skimmer, but you may want to 'forecast' your future intentions and elect to go ahead and purchase more 'reef ready' filtration right now. The best will be a sump of some sort, wet-dry or not, that you can convert to a 'living sump'/refugium down the line.

            It's a good idea to  provide a bit of redundancy in your filtration/aeration/circulation system/s, and so do consider adding an outside power filter, powerhead/s or submersible pump/s just in case one of your other mechanicals fails.

            For large/r systems with lots of large, dirty fishes intended, you will likely need some added physical/mechanical filtration. This can be provided by a variety of cartridge or canister filters, equipped with their own pumping mechanism. Their big downside is the frequency of cleaning necessary'¦ likely at least weekly.

            Some folks opt to provide an ultraviolet sterilizer, ozonizer (maybe even with a dryer), live rock et al. in their FO system set-ups'¦ these are very useful adjuncts to an otherwise properly/adequately arranged system.

Lights/Lighting: For Fish Only systems is very simple. Basically this comprises what suits you, the aquarist, in terms of brightness and color-rendering. Do pay attention to the myriad choices in lamp types'¦ Likely, unless your system is very large (More than a hundred gallons), some form of Normal Output to boosted fluorescent technology will do here. However, once again, if you think you might be going to 'reef' in time, you may want to jump ahead and invest in a type of lighting that will serve your needs with photosynthetic life. Do pay attention to not just the install/gear purchase price but the ongoing energy consumption and lamp replacement costs. This can be the single largest ongoing expense in keeping an aquarium.

Substrates/Gravel: There are some folks that eschew using gravel in FO systems, claiming that this makes it easier to keep the tank clean, but having gravel does so much for water chemistry and providing habitat (and eliminating bottom reflection that bothers fishes) that having at least some is strongly encouraged. For functional reasons, either an inch or less, or a few inches (4-5 or more) is better than an intermediate value. The thicker is best employed where keeping burrowing fishes like Jawfishes.

            About a pound per gallon will likely do for the smaller value and not to worry re. You can always add more to what you have if you'd like, as time goes by.

Heat/Heating:  Marine environments are noted for their stability/constancy, including their thermal make-up. You'll need a reliable means of providing tropical temperature with your FO set-up'¦ likely a hang-on or submersible heater or two, depending on the size of the tank. For sizing, a handful of watts per gallon are about right. Oh, and of course you'll need a way of measuring heat content'¦ a thermometer'¦ perhaps a 'stick-on' variety for in/outside the tank. Avoid glass, floating ones as these are easily broken by some fishes and hobbyists.

Décor Items: You might think that such things as base rock, coral skeletons, shells, plastic plants and such are unnecessary for Fish Only systems. This is assuredly not so. Having décor in the tank does much to break up the physical environment, reduce aggression, provide surface area for beneficial microbial habitat'¦ and it makes your tank look great! Do plan on having purposeful ornaments, additions in your FO set-up'¦ that are either chemically non-reactive, or that impart desired qualities to your water.

About Water, SeaWater, Testing: Unless you can secure clean, pollution-free natural seawater you'll want to plan on buying synthetic salt mix, a means of mixing/storing it, testing its concentration (likely by specific gravity) with a hydrometer'¦ Look to buying in bulk here'¦ the 'bucket' quantities are the cheapest, and it's nice to have the buckets about for dedicated pet-fish use.

            Your tapwater may need to be treated as well'¦ With a dechloraminator, to remove sanitizer that mains/source water is treated with to make it potable.

Water Quality Test Kits: For FO systems you will likely need to test for the 'cycling' issues of ammonia, nitrite and nitrate, as well as pH and possibly the measure of its 'steadiness', alkalinity. These tests/kits will give you insight into what is going on in/with your water and aid you in determining how much, how often to perform water changes, switching out of filter media to keep your water clean. Simple colorimetric kits exist, separately for individual qualities, or grouped as 'master' kits for a few types of testing.

About Electricity: There is definite danger with having aquariums, particularly saltwater aquariums around electrical outlets'¦ and you'll have these plugged into the wall'¦ and in your tank! Do make sure that all circuits are GFCI protected, or alternatively purchase a GFCI type multiple outlet strip to prevent electrocution and/or electrical fire.

Some 'Extra'/Misc. Gear: You'll want at least two nets (best for catching fast fishes), one large/r, one small/er, a gravel vacuum, an algae scrubbing pad, likely some replacement filter pad/s and media'¦ as well as dedicated buckets, towels for your own pet-fish use. There is a seemingly endless list of extras we could go on with'¦

Conclusion: 

            Though Fish Only systems are the simplest, introductory types of saltwater aquariums to 'get into' the hobby there is still a great deal to consider in putting together the choices of gear available. Will you 'go reef' eventually? If you're not sure, or pretty assured the answer is no, then you may save a good deal of time, effort and money and secure 'just adequate' equipment for a FO rig'¦ On the other hand, if there's some doubt, notion that you might want marine invertebrates, algae, more delicate fish life'¦ it would serve you well to delve into/investigate more 'reef' gear from the get-go.

Small Marine Aquariums Book 1: Invertebrates, Algae New Print and eBook on Amazon: by Robert (Bob) Fenner	Small Marine Aquariums Book 2: Fishes New Print and eBook on Amazon: by Robert (Bob) Fenner	Small Marine Aquariums Book 3: Systems New Print and eBook on Amazon: by Robert (Bob) Fenner