So you want to start a saltwater tank? Awesome and good for you! You don't need to have FW experience, but a little understanding goes a LONG way. Here is a brief summary of things to consider when starting a SW tank. This is in no way a complete list, it's just a list of the most basic things you need to consider when starting a salt tank. Be sure to read up on topics and do plenty of research before starting anything because salt tanks are more costly then fresh. Tank Size As with freshwater, the bigger the better. I would look into purchasing the biggest tank you can afford and fit into your desired location. A larger tank has a larger water volume which means more stable water parameters. If something goes wrong in your tank it will happen a lot slower in a larger tank then in a smaller tank. I would suggest no smaller then 30 gallons for your first tank. Tanks smaller then 30 gallons will work but they should be kept by more experienced fish keepers. Tank Types & Live Stock Tank types of stocking go hand in hand. You need to consider both items when starting your tank. There are 3 types of SW tanks which I'll list below. 1) Fish Only (FO) - Just as the title says, these tanks only have fish. This is the least desirable SW tank and you won't find too many of them. These are the basically the same as a plain FW tank. You can keep any fish in this tank as long as it's compatible with your other fish and is not too large for your tank. 2) Fish Only With Live Rock (FOWLR) - These tanks have fish but also have the addition of live rock. Live rock isn't living itself. It is called live rock because of the bacteria and other living things living in and on the rock. Live rock will be your MAIN filtration in the tank and also be a food source for some of your live stock because they will graze on some of the critters on the rock. For more information on live rock, visit the live rock wiki. You can keep any fish in here as long as it's compatible with your other fish and is not too large for your tank. 3) Reef - These are going to be just like a FOWLR tank but they will have the addition of corals and anemones. For the most part, corals need pristine water conditions so the amount of fish in a reef tank is less than a FOWLR. You really need to do research when starting a reef tank. Many fish are not reef safe because they may nip at your corals as a food source. Also, different corals require different levels of light so you are going to need to purchase a better light fixture such as T5, metal halide or reef supporting LED's. You really need to do some research when deciding on your tank. You may really want a reef tank but one of the fish you want may eat your corals. You have to decide if the fish or the reef is more important at that point. I suggest to write a list of fish you would like and then write down next to each one whether it's reef safe or not. Then make your decision. You can always start with a FOWLR and convert to a reef later on too. Water Do not use tap water. Just don't do it. If you want a SW tank then use RODI water. RODI water stands for Reverse Osmosis Deionized water. Tap water contains chemicals to help keep the water safe for us. These items are NOT good for your fish though. An RODI unit is basically a Brita water filter on steroids. lol It pretty much removes everything from the water and leaves you with almost pure water. I bought an RODI unit myself but some people choose to purchase it from their LFS. The LFS will sell you this water for around .50 a gallon Some people also choose to use natural sea water from the ocean. While this may work for some people, I don't want to suggest it because the water quality in unknown. Too much pollution in the water for my tastes. You need to keep that water level in your tank consistent too. That's because as your water evaporates, the salt remains in the tank. If you have experience with a FW tank and nitrates then it's the same principle where only the water evaporates and everything else gets left behind in the tank. The salt level in the tank will rise as the water evaporates so you need to keep the water level in check. When adding top off water to your tank you are only adding FRESH RODI water. You do NOT add salt water when topping off your tank. The only time you add salt water to your tank is when doing a water change. Equipment There are many types of equipment you can have but here's a rundown of the basics. 1) Lighting - A fish only or FOWLR tank can use standard florescent lighting if you so desire. A reef tank with corals needs stronger lighting because corals rely on photosynthesis, just like a plant does. These inhabitants need light similar to natural sunlight to survive. These fixtures are T5's, metal halide and reef supporting LED's. Your tank depth, inhabitant needs and your wallet will be your deciding factor. There are way too many factors to say which one is best for you but here's an outline. Different corals have different light needs. T5 lights are great for tanks that aren't too deep while metal halides are best for deeper tanks. That's because the light output from a metal halide penetrates the water much deeper than a T5. What that means is say you have a coral that requires a strong light source. If you have a T5 then you might have to place that coral on some live rock towards the top of the tank because that's where the light is the strongest. If you have a metal halide then you could place that coral at the bottom of the tank since the usable light from the metal halide penetrates deeper than a T5. There's a lot more to consider but I just wanted to give a little overview. 2) Filtration - I would skip the fish only tank and go right to a FOWLR or reef. That's because live rock will be your main filtration. The bacteria in the nitrogen cycle colonize the rock and do all the chemical conversions. You need enough live rock to accomplish this so plan on about 1.2-1.5 lbs of live rock per gallon of water. A protein skimmer is also a great investment. This unit removes organic compounds from the water before they get broken down to nitrogenous waste. A good rule of thumb is to get a skimmer for DOUBLE your tank capacity. If you have a 50 gallon tank then get a skimmer rated for 100 gallons. A 200 gallon tank, then get a skimmer rated for 400 gallons. 3) Water flow - Water flow is very important. Your fish like to swim through the water flow, but more importantly is helps in your filtration. Your water needs to pass over your live rock in order for it to process the waste. In a FOWLR tank you want about 10-20X water flow for your tank size. That means for a 30 gallon tank you want water flow of 300-600 GPH. This water flow is calculated by adding up the gph produced by the equipment in your tank such as powerheads, filters and skimmers. Say you have a 400 gph powerhead, a 150 gph skimmer and a return pump for 300 gph. That would give you a turnover rate of 850 gph in your tank. It's also a great idea to position a powerhead towards the water surface to help agitate the water. This will provide much great surface area for the water and air to mix and will aid in oxygenating your tank. A reef tank requires more flow in the neighborhood of 20X and up. That's because corals filter the water and get some of their food by filter feeding. There are many routes to go with water flow, it really depends on your tank type and inhabitants. 4) Substrate - There are 3 methods for the bottom of your tank which are shallow sand beds, deep sand beds and bare bottom. Shallow sand beds are generally about 4" deep or less. These are used so you are not looking at a glass bottom tank. Certain tank inhabitants also like to burrow and dig through this. Deep sand beds are IMHO, the least eye pleasing. These are generally about 6" deep, but the great thing about them is that they can help remove nitrates from your water. Again, some inhabitants like to burrow and dig into it. A deep sand bed does require some work and a small portion of it should be disturbed every so often to help keep the tank in order. Bad things happen in a deep sand bed that doesn't' get disturbed. Bare bottom tanks have no substrate at all. These are generally chosen by individuals wishing to keep corals that require very high flow rates. High flow rates can kick up your substrate and push it all over your tank and cover your corals. A bare bottom is the easiest to clean since the detritus doesn't have a place to accumulate. 5) Sumps - These are great for your system because they add to the overall water volume which means more stable conditions. They're also great because you can place your protein skimmer and heaters in there so they are not visible in your main tank. It makes for a much nicer presentation. You can even use carbon and other filter media in your sump if you so desire but be careful with mechanical media with a reef tank. Mechanical media must be cleaned every few days or it will cause a nitrate spike. Lower nitrate levels are OK with FOWLR setups but a reef setup should be at about ZERO for nitrates. You can even place more live rock in a sump for more filtration. 6) Refugiums (Fuges) - Fuges can be part of the sump, replace a sump or another separate tank. Fuges are a great addition because like a sump, they increase water volume. Another great thing is that you can add a deep sand bed in a fuge to help reduce nitrates. This is great if you choose a shallow sand bed or bare bottom tank. A fuge also lets you grow macroalgae in an area that is protected from fish. Macroalgae will take up nitrates from your water. Amphipods and copepods can also be grown in a fuge. These are little crustaceans that can clean up detritus and also be a food source for your fish. These pods grow in the fuge and some will end up in your main tank. More info on pods. You don't need a sump or a fuge but they help. You DO need a fuge with a large supply of pods if you choose a fish like a Mandarin which feeds almost exclusively on pods. You may be fine without a fuge if you have a Madarin in a tank of 75+ gallons with a lot of live rock though. 7) Testing - Purchase a good test kit like an API or more expensive like a Salifert. I also suggest purchasing a refractometer instead of using a hydrometer to measure your salt content. Stay away from test kits that use strips. 8) Heaters - This goes for SW and FW tanks. The rule of thumb is to get 3W per gallon. So if you need 300W of heating, don't purchase a sinlge 300W heater. Purchase 2 150W or 3 100W heaters. If a heater gets stuck in the ON position then you are going to cook your tank VERY quickly with a 300W heater but you'll have plenty of time to catch it if you use a number of smaller heaters. 9) Other Items- There are a slew of other equipment that can be used in a SW tank such as calcium reactors, UV sterilizers, kalk, auto top offs, chillers and more. You don't necessarily need these items at the start, or even at all. As I mentioned above, this is not a complete list by any means but I hope it answers some basic questions and clears some things up. All of the above items can be discussed in much greater detail and I hope that my information above leads to more questions and more research. You need to go VERY slow in this hobby. I've read too many posts about people having problems and it's because they have 5 fish in a tank that's only 2 months old. Good luck!