As far as the fish go :-
The clown fish is/are fine. In the Finding Nemo tank, there's also a yellow tang (fine), a moorish idol (stay away from it, although they're awesome to look at!), and a couple of others.
Dori is a Regal Tang, which should really be kept in a 75gal+ aquarium, and ideally not with another tang (ie. the yellow), but in a bigger aquarium, with the 2 tangs being very different colours/shapes, it shouldn't pose much of a problem.
As for your filter, it will work, but it probably won't be very effective.
A lot of people just use live rock for filtration, but there are a lot of choices. Eheim make some great external wet/dry canister filters, and a lot of people go for a sump. Whatever you do, go for "too much" filtration rather than skimping on it.
Of course, you'll need a synthetic salt mixture for your water, and a whole host of test kits to check how everything is going - both in the initial cycle (the stage before you can put any fish in, when the bacteria are getting colonised in the tank), and on-going. Get kits for:- Ammonia, Nitrites, Nitrates and pH at the very least. I'd also recommend an alkalinity, or carbonate hardness test - if these are at a good level, your tank will resist downward changes in pH much better, and the pH will remain much more stable - pH goes down over time, and a drastic or quick change in pH can be fatal to your fish! You'll also need a hydrometer or refractomer to check the level of salt in your water, which needs to be kept at a specific and steady level.
I'd use live sand as your substrate - it not only looks nice, but also comes with heaps of bacteria to help your tank!
You also need lighting, of course. If you're only intending on keeping fish (and not corals etc.), then the lighting isn't as crucial. Water circulation/oxygenation is also important - invest in a couple of powerheads to create waterflow.
Then, you need hiding places for your fish. Get some liverock - this not only looks nice, and provides hiding places (makes your fish happier!) but will also help in creating a full eco-system in your tank. Also, plants/fake corals etc. are nice.
You'll also need to think about your water source, both for the initial fill up and waterchanges - tap water will more than likely contain far too many Total Dissolved Solids (TDS
) - a normal water filter for home use reduces these down, but marine fish are very sensitive to this aspect. A Reverse Osmosis (RO
) unit is a very high quality, effective "filter", which will take the majority of the TDS
's out of your tap water, making it suitable for aquarium use. An RO
(De-ionisation) unit is by far the best option, as it has a seperate section to treat the water "again", but these can be expensive. You can usually get RO
water ready-made from your LFS
, if you decide to skip this. Depending on how close you are to your LFS
, and their opening times etc.
As well as filtration, a lot of people also use a protein skimmer, which removes dissolved organic wastes, helping your water quality further.
So, you need to "Cycle" your tank first, which means before you put any fish in (but everything else is up and running, bar the skimmer, if you go for one) you have to establish the bacteria in the tank that make everything work. Fish waste and/or uneaten food create ammonia, which even in small doses is fatal to marine fish. The first lot of bacteria convert this ammonia to nitrite, which also in small doses is fatal to marine fish. Then, a 2nd set of bacteria convert the nitrites to nitrate, which is less harmful to fish, but should still be kept as low as possible through water changes etc. The final stage is converting to nitrogen gas and leaving the tank.
To do this, a lot of people use a raw shrimp as the ammonia source - you have to wait from 2 - 6 weeks (basically until your ammonia has gone up and then down, nitrite has gone up and then down, and nitrates are then creeping up slowly) to cycle the tank. Test regularly with your kits so you know what's going on. One you've cycled, as long as you don't overload the tank with too many fish, too many fish added at a time, or overfeeding etc., these bacteria are living in big enough numbers to constantly convert am - nit - nat so that you should never seen them again.
A week or two after you've cycled, take the shrimp out and add a few bits of food every couple of days to keep the bacteria alive. Then, if all is ok, you can add a small fish or two. I'd then wait for quite a while (1-2 months) before adding any more fish, to let your tank further stabilise and to learn about it's workings. I'd also get some fairly hardy fishes as the first ones - 1 or 2 percula clowns (nemo/dad!) would be perfect. Then stock slowly over 4 - 12 months - the longer the better really! Also take note of the order of adding fish so as to give your tank and it's inhabitants the best chance of getting on well!
The main thing is patience - add fish very slowly, and keep a very close eye on them. Don't overfeed, and be very vigilant.
It's a very big subject - I'd get a copy of The Conscientious Marine Aquarist by Robert Fenner (http://www.amazon.com/exec/obidos/tg...books&n=507846
) - this has helped me no end!
Before you do anything, read up and research. Then, when you actually get your tank, the learning will REALLY begin!
Main thing - patience! I didn't have this virtue before I started in the hobby, but I'm slowly learning it!
Good luck, and have fun!