Plants in SW for the most part is algae. Most of the nicer algae is actually pretty difficult to care for, as odd as that may sound. Soft corals are, in my opinion, actually easier to keep than most macro algae that one would use in a display tank. The easier macro algae, like chaeto and caulerpa is easy to grow, but extremely invasive in a display tank and is used for nutrient reduction in sumps. The only "plant" that I know of that is common in SW are Mangroves. There are also sea grasses but those seem to be difficult to keep. Amphiprion on here has a sea grass tank going, I believe a 25G tank with an MP40 powerhead (up to 3000 GPH) and he has difficulty keeping some grasses alive and has said the flow is very limiting when the grass grows in.
Plants for SW links
http://www.saltwaterfish.com/Plants_c_44.html
http://reefcleaners.org/index.php?page=shop.browse&category_id=6&option=com_virtuemart&Itemid=34
The best advice I think to give anyone, is start out as slow as possible. If it takes a year to get the tank going with rock, filters, flow, and lighting, that really just helps the tank mature. The instinct everyone has of wanting to rush out and put a fish in the tank is the worst thing to do. To be the most successful I think fish should be one of the last things to put into a tank after doing LOTS of research on what fish you want and compatibility with your system. To start out a 120G on a limited budget to ensure the most success with livestock I would first add a few pieces of rock, at least one piece being live rock to seed the others, sand, the biggest powerhead you can afford, heater, and standard light.
You want to get the aquarium from sterile to habitable and with just a single piece of good live rock and lots of time and patience, that will get the tank started. After the tank is started I would add dry rock as $ allows until you feel you have enough. I would say 50-60lbs would be a good goal for what you want to do. Once you have added all the rock and let it mature for a couple months (it takes time for dry rock to become live again), work on getting the rest of the equipment you will need, light, powerheads, filtration. The standard light that comes with it is fine for getting the tank cycled and for a fish only tank, but for corals your going to need more. If your just going to focus on soft corals, mushrooms, xenia, green star polyps, all of which are the best type of coral around predators as they tend not to touch them, then you could get by with a 150 MH, or LEDs, or about 4 24" T5HOs. During this time of getting equipment you can add a couple snails, crabs, etc to give you something to look at and to help clean the tank some.. but they will become lunch to eels and puffers so don't spend a lot of $ on a clean up crew if your plans are for predator fish.
Plants for SW links
http://www.saltwaterfish.com/Plants_c_44.html
http://reefcleaners.org/index.php?page=shop.browse&category_id=6&option=com_virtuemart&Itemid=34
The best advice I think to give anyone, is start out as slow as possible. If it takes a year to get the tank going with rock, filters, flow, and lighting, that really just helps the tank mature. The instinct everyone has of wanting to rush out and put a fish in the tank is the worst thing to do. To be the most successful I think fish should be one of the last things to put into a tank after doing LOTS of research on what fish you want and compatibility with your system. To start out a 120G on a limited budget to ensure the most success with livestock I would first add a few pieces of rock, at least one piece being live rock to seed the others, sand, the biggest powerhead you can afford, heater, and standard light.
You want to get the aquarium from sterile to habitable and with just a single piece of good live rock and lots of time and patience, that will get the tank started. After the tank is started I would add dry rock as $ allows until you feel you have enough. I would say 50-60lbs would be a good goal for what you want to do. Once you have added all the rock and let it mature for a couple months (it takes time for dry rock to become live again), work on getting the rest of the equipment you will need, light, powerheads, filtration. The standard light that comes with it is fine for getting the tank cycled and for a fish only tank, but for corals your going to need more. If your just going to focus on soft corals, mushrooms, xenia, green star polyps, all of which are the best type of coral around predators as they tend not to touch them, then you could get by with a 150 MH, or LEDs, or about 4 24" T5HOs. During this time of getting equipment you can add a couple snails, crabs, etc to give you something to look at and to help clean the tank some.. but they will become lunch to eels and puffers so don't spend a lot of $ on a clean up crew if your plans are for predator fish.