Since everyone's taste is different, I guess you should choose your own fish to keep. Theres no point to keep a certain fish just because some website says a beginner should keep this fish. However, you are recommened not to get any fish on impulse. Read up on its diet and requirements first, and see if you are able to meet them. Also note whether it is a territorial fish or a community fish, whether it prefers to have a school of them or whether it prefers to stay with only a few companions.
When you decided what fish to keep, you select your fish using this rules
- fish should be swimming around, not hiding
- no abnormal coloration, even if its a small patch
- no cottony stuff anywhere
- look at its breathing, does it look relaxed or out of breath
- if its keeping to itself instead of mingling with the rest it could be sick
Never ask the store keeper to just bag any fish because he will be bagging the inactives one that is easier for him/her to catch, exactly those that you want to avoid.
Number of Fish
Always add fish slowly so that your biological filtration has time to adjust to the increased bioload. Test the water for ammonia and nitrites. If they are under control, you can add more fish. If they are slowly rising, give it time. If they continue to rise, add more bio media. In short, the number of fish you can keep is limited only by your filtration. There is really no rule of the thumb as to how many fish in how many gallon of water unless you are living in the dark ages where people does not know about bio filtration and change water everyday. At that time, you need a water volume for every inch of fish so that it acts as a buffer for the waste buildup until the next water change.
Acclimatize Fish to Aquarium
In layman terms, it means letting your fish adapt to the differences in water conditions from the water it was living in at the store, to the water in your tank. There is no set sequence, you just need to remember 2 factors. 1 is temperature, 2 is water. Temperature is usually not a problem if your aquarium is in normal room temperature (ie no air conditioning nor heating in your room. This is because if the fish was living in a place with a different temperature, it would normally have adjusted to the outside temperature by the time you get back home. The other differences it has to adjust to is pH, hardness, salinity etc. Give your fish as much time as possible to adjust. The limitation is only your patience.
The process is to slowly make the water in the holding bag be the same as the water in your tank.
1. Take some water from your tank and add it to the holding bag.
2. Let the water added mix with the the water in your holding bag.
3. Take some water from your holding bag throw away. (so it doesnt overflow).
repeat step 1 to 3 over and over again until you run out of patience
4. Net the fish and throw away the holding bag and whatever water left in it.
Note: It is important that you throw the water away in step 3 instead of pouring it easily into your tank because the water in the holding bag comes from the store, and it can contain diseases and parasites just waiting to strike! The best way is to prepare a pail/bucket handy where you can pour the water to.