There is an unsaid rule in the saltwater aquarium hobby which is that the smaller the harder and the bigger the easier.
What that translates into is that smaller tanks are harder to keep going. The reason for that is because it's much easier for your levels to get out of balance in smaller tanks. And, we all know what happens once your levels become unstable. It usually results in a loss of life and a great amount of tragic flushing.
With that being said, let me give you a couple of pointers about getting your first tank.
1. Be Prepared to spend at the bare Minimum $500 - $1000 dollars.
Bigger the easier, also means the more you initially will need to spend on a tank. But, if you want your tank to thrive and survive, and it may seem like a lot at first, but it is well worth the value after seeing your tanks flourishing' success.
2. Populate your tank slowly over time. Do not rush the Process.
Once your empty tank is ready for life. Start with some live rock, snails, baby starfish, maybe shrimp and other bottom feeders. After a week or so of letting your tank cycle, you can then begin to add some easy coral like mushroom, leather or star polyps. Once you see that they are thriving, now it's time to add some fish such as Clown, Anemone Fish or Chromis.
3. Hire a tank professional from your local saltwater store to get it going and maintain it for the first 6 months.
Don't risk the chance of ruining your new tank by making rookie mistakes and sure don't bet your aquarium's life on it. Most local fish stores offer tank maintenance for around $150 bucks a visit depending on the size of your tank. Your fish pets will thank you for it later I promise.
4. Start off with easy Coral and Easy fish.
In the aforementioned tip #2, Easy coral you can start off with are mushroom, leather or star polyps and some beginner fish to put in your tank are Clown, Anemone Fish or Chromis.
5. A drilled tank is much better than a hang on overflow.
When it comes to water filtration, you can either have your tank drilled or drop in a hang-on overflow. If you are getting a big tank of 50 gallons or more you should most likely have a drilled tank. Small tanks with an overhead are not impossible to maintain but the are the more difficult ones to keep thriving.
6. Have sump and/or other filtration systems.
Just as a consequence of natural processes, your tank is going to need filtration systems. Whether it's to get rid of a build up of algae (which you will also need to literally scrape off your tank every week,) or just a build up of nitrates from anything that may have died unnoticed or from fish waste; these things must be filtered out. Having a sump and other filtration systems is, in most cases, almost absolutely necessary.
7. Do not put fish and coral together that cause conflict to other fish and coral. I don't care how pretty something looks.
Sometimes we see something in other people's tanks or online that looks really awesome and we really want it whether that be a shark, an eel, or some awesome looking, but aggressive coral or other fish, but that doesn't mean we should just go throw anything in our tank because it looks colorful and bold. This can spell out trouble for your other sea life if you aren't careful about what you put in your tank. Google before you drop.
8. You will need a lighting system.
Without UV lights, you are dead, so of course, your coral and fish will be too. All life on Earth is dependent on UV light cycles. That's how you get your Vitamin D and that's how plants produce their energy that provides food for the rest of us. Coral are especially dependent upon this UV light cycle being as natural as possible. Make sure you have lighting system that either you have timed yourself or that you have in a timed lighting system.
9. Pay attention to your fish's behavior and look.
Your fish's behavior can tell you a lot about what is going on in your tank. They can also tell you if your tank has been infected by something like a parasite, bacteria or otherwise. If you see a fish swimming upside down, it is not trying to entertain you. Some of these products could help.
10. Consider upgrading to a bigger tank.
If you started off with a relatively smaller tank, you might want to start thinking about moving to a bigger tank, especially if your tank isn't a drilled one - that is unless you are specializing in Nano-tanks and your knowledge is on expert level. Remember the longer you keep your tank, the more you have invested in it. Don't let your hard work go to waste by letting a smaller tank go south over night.
11. Don't let your Temperature fluctuate too much
The temperature of your tank is crucial. You should absolutely have temperature regulator. In a time of climate change, it has been shown that sea life does not like drastic swings in temperature. If your tank gets too hot too quickly, your coral will suffer a great whitening, i.e., die. Invest in a temperature regulator.