First piece of advice - always always always buy the biggest tank you can afford. You won't be able to add any more fish than what you have so far. Rule of thumb is 3-5 gallons of water per fish. Here's what you need to do for a water change (posted by squid)
- Aerating the water while mixing does a couple of things that are beneficial for your tank and aid in a proper balance of elements in the finished water.
First of all you are starting with "dead" or unoxygenated water...Water form a well or in the pipes of a city system is generally not exposed to air (contamination reasons) so it comes from the faucet (or through your RO/DI) with a relatively low DOC (dissolved oxygen content).
Dissolved oxygen is what the fish "breath" and aerating it for a good period of time adds this "breathable' oxygen back.
Secondly when mixing salt to water you should aerate the water for a period of time BEFORE adding the salt.
There are actually two points here...If you have ever looked at the threads on alkalinity and calcium you've seen how they need to stay within a specific balance of each other or they combine into other forms and precipitate out...one gets too high (saturated) and effects the other...
By adding the salt to the water you are mixing at diluted levels and bringing them up to the specific gravity level they will remain in suspension...
If you were to start with the salt and add water to it you would have a super saturated mix that would react to itself and some parts would precipitate out as calcium carbonate.
The second point is related to the first in that specific carbon dioxide and oxygen levels are needed (not present in un-aerated water) to keep the calcium and alk/buffers in suspension.
This is why "NEW" salt water is considered "chemically unstable" and should be mixed AND aerated for 24 hrs. prior to adding to your tank... In order for all "balances" to come in line and any precipatate to "fall out" in your mixing bucket and not your tank.
It does make a difference and your fish (and corals) will thank you for it.
As for how much salt, it should say on the package of salt. Instant ocean is 1/3 cup per gallon i think. DON'T use table salt. I'm serious, it's been asked before.
Also, you will need some way of heating the water that goes into your tank. By setting a bucket in the bathtub filled with hot water should do the trick. When the temp is between 78-80, you can add the salt. Also check the salinity before adding it to your tank. The Salinity should be around 1.023 plus or minus one.
Also, you did not mention whether or not you had a heater for your tank. Some people need one and others don't. You can buy a thermometer that either floats in the water or sticks to the outside of the tank.
You will need to change about 20-30 % of the water/month. This is a heated debate. Do a search and you can find lots of different theories. Try one and see which one works best for you.
You need test kits. The more the better, but definately need Ammonia, Nitrite, Nitrate, and pH. Ammonia nd Nitrite should always be 0, nitrate no more than 40 (otherwise you need to do a water change) and pH at about 8-8.3 T
This sounds like a lot of stuff, but that's just how this hobby is. If you have any more questions, feel free to ask. That's what this board is for.