As basics, you need a filter, heater, thermometre, hood, lighting, substrate and decorations.
Filter - for a basic tank (not heavily stocked, no super-messy fish, not heavily planted) I'd recommend a filter that can turn over 5 x the volume of the tank per hour. For a more hevily stocked tank with plants and messy fish, I would recommend 10 x. For 180 litre tank, check out the external filters on offer. Brands include Rena, Eheim, Fluval and Tetra, but there are others. Don't be tempted by an internal filter in a tank of that size, unless it is "as well as" rather than "instead of" a larger filter. Sumps are good but not necessary. If you're interested, check out the equipment and DIY forums.
Heater - you want one rated for your tank, probably a 200-300W heater. Where possible, get two smaller heaters rather than one big one so you have a back-up if one fails. Always use a seperate thermometre as well. Digital or traditional glass ones are best - I really don't rate the liquid crystal stick on ones.
Hood - try to get a second hand hood that is built for your tank. Failing that, consider a simple sheet of glass or even a DIY hood. Loads of info online about how to make your own gear. Hoods help prevent envaporation, give you somewhere to house your lights and stop things getting into the tank. Also stop fish jumping out!
Lighting - depends on your needs. Some fish and plants actually prefer very low light conditions while some want it bright. Lighting is a whole issue that needs careful research. For a basic tank, consider two UV T8 'daylight' tubes. These will be fine for the fish and will mean hardy plants will grow. Tubes need controller kits and these can be bought (Arcadia are a popular brand) or made (check out the DIY section and other online resources).
Substrate - depends on the fish and plants. For bottom feeders that like to dig or sift, sand is best. For larger bottom feeders that don't dig much but still want somethiong smooth, get sand or very fine, smooth gravel. For larger fish that like to move decor around, get something that they won't get stuck in their mouths. I would always advise a darker substrate as this helps fish feel more secure and at home in the tank. Plants like anything from fine gravel to sand, but probably won't thrive in chunky gravel. If you really want to go to town with a heavily planted tank, consider a dedicated planting substrate like Eco-Complete
Decorations - I prefer bio-tope/natural decor. This means that if I have fish that live in rocky water with no plants, I don't put them in a planted tank. This means that fish that like lots of wood in the wild get lots of wood. Etc. The more natural the tank and the more it resembles the natural environment of the fish, the more secure the fish will feel and the more likely they are to be healthy, active and behave naturally and be stress free (all other things being equal). Even if you prefer a more artificial tank (fake coral, bridges, castles, etc) try to get stuff in muted colours and that gives the fish plenty of hiding places. Also don't try to get fish that you know won't like the tank - I.e. don't fill the tank full of bright pink plastic decorations and then put a load of shell dwellers in there. It does mean a lot of reading but you'll soon find that fishkeeping is about the reading and research, LOL!
So, those are the basics. The bestplaces to get gear depends on your budget. Local adds, Freecycle, Ebay, local shops, online. It totally depends on whether you want new or second hand and how much you have to spend. I recently got a 290 litre fully planted tank with gear worth at least £1500 for free on Freecycle so there are serious bargains to be had.
To start out, I would buy new as you have a better chance of getting something that works well and have a warranty. However, I started out second hand and so far have not had a filter/heater/tank die on me. *touches wood*
However - and it's a BIG however - don't do anything without researching. Before you get your equipment and put money down, find out what you want and where to get it from. Read reviews, make sure you know what your gear is capable of. Same goes for setting up the tank and getting fish.The last thing you want to do is say get a lobster and find that after 2 months all your fish are bitten, eaten or stressed because of the beast. That was my way of saying avoid lobsters with fish, lol. Don't trust retailers for info - listen to what they say but then double check in books and online.
Here are a few things to research -
Fish - types of fish, their water needs (ph, hardness, water flow, temperature), their social needs (solitary, loose groups, tight shoals, etc), their dietry needs (slow bottom feeders vs high speed surface feeders don't tend to mix, etc), their eventual size, their agression levels . . . anything and everything. The key to a healthy tank is fish that have similar needs. You don't want to put a fish that likes cold, hard, alkaline water in with ones that like warm, acidic, soft water. You don't want to put large fish in small tanks (even if they are cute and small in the shop) and you don't want to put fish in with those that will attack or eat them.
Water - you MUST (must must must!) researchabout the aquarium nitrogen cycle. Read about the cycle and different methods - including fishless and fish-in cycles. Without knowing about this you will get into major trouble as your water will turn toxic and your fish will suffer horribly. Research, research, research! Helpfully, in the New Tank section there are some excellent articles in the Resource Centre. Go look NOW! You need to be prepared to test and change your water regularly and know the pH and hardness of your water so you can maintain suitable fish.
Plants - if you want like plants you need to remember that they are not just decorations but other living things. They need the right care or they will die. Dead plants, aside from being a shame and a waste - look awful and pollute the tank water. There are plenty of hardly, easy plants out there so research before rushing in and buying something. No point shelling out £10 for a lovely potted plant to find that it just won't thrive in your tank.
Based on your fish-list, here are some pointers -
Clown fish - what do you mean? Clown fish are marine (so will die in freshwater) but you might have mixed them up with clown plecs or clown loches? Clown loaches get too big at 12" adult size so some yo-yo loaches (6" adult size) are the biggest loaches I'd recommend for your tank. Better still are loaches that get to 2-4" adult size. For example, a large group of dwarf chain loaches would be awesome! If you're talking about a clown plec, that shou;d be fine as I don't think they get very big. Here are two great websites for info about
catfish and
loaches.
Tetras - most tetras are small enough for your tank. Each species should be kept in a group of 6-8 and few large groups looks better than loads of small groups. The fish will reward you with beautiful, natural behaviour and bright colours. Always do your research, even with seemingly "common" or "easy" fish like neon tetras.
Lobsters and Shrimp - NO. Shrimps are good alternatives if you like the invert look. Amano shrimp are hardy and not too small but also pale. Make good clean-up crew members. Smaller but bright shrimp include cherry shrimp. Again, find a dedicated shrimp website and have a good read about the different options and their needs.
