Before buying a filter, a heater, or any other lifeless piece of equipment, it may be of some use to do a little research, just so you buy the right one. However, when buying livestock, that is fish and invertebrates, you need to research thoroughly before you buy. This is essential in order to avoid unnecessary suffering and death in your aquarium. Here's what you need to know before buying a new fish or invertebrate.
The first thing you need to know are the water requirements for the animal in question. You need to be absolutely sure that it is either suitable for the water your current fish are swimming around in or, if possible, that you can provide water with the parameters it needs in a new aquarium. This includes the Ph, hardness, temperature, oxygen levels, and salinity. The water parameters must be suitable for ALL of the fish housed in any single aquarium. An average will not always work, especially for particular and demanding species.
Size is something else you may with to devote some attention to. If your aquarium is a small 10 gallon tank, it would be foolish to think you could keep something that grows large, like many catfish species or a pleco in there without having to give it away when it gets too big. Maximum sizes are given in pet shops for a good reason, it's so you don't buy a fish that busts its way through your tank.
You must also ensure that the animal you are wishing to add to your collection is compatible with your other fish. Numerous deaths occur in aquariums without the owner ever realising. Many of these are down to smaller fish being eaten by larger ones. Avoid putting fish into tanks in which they'll make a tasty snack to a predator. Instead, choose suitable species that compliment one another. Be sure to spare a thought for stocking numbers too as you won't want your water quality deteriorating due to overpopulation.
Check out reproduction rates and diseases too as these can ruin an aquarium. A fish that won't stop breeding can leave you with hundreds of fish you have nowhere to keep and no means of giving them away quickly enough. A disease prone species can be irritating, especially if you have invertebrates in your tank that'll be killed off by the copper found in many fish medications.
This article is by Steven Caller, Editor of Aquarist Magazine.