Choosing fish for a tropical aquarium

Before you even think about fish, you should buy a test kit (the liquid ones are often more accurate) to test for the pH of the water. These can be bought in all fish shops cheaply and are very easy to use, just follow the instructions.
A pH below 7 is acidic, above 7 is alkaline, and exactly 7 is neutral. This will be shown by a colour chart, with green being pH 7.

The pH of your water is important to know, as some fish need more acidic or alkaline water, though most are fine living in water of a pH between 6 and 8. Slightly acidic water is best for most fish, so if you're struggling with high pH, here are some methods with which to lower the pH.

Obviously, the number of fish you can have depends on the volume of water you have, so do widthxheighxlength to calculate the volume. You also need to factor in the shape of your tank. Most larger tanks are long, rectangular shape, which is best for the fish, though smaller tanks are often tall, which can restrict the type as well as size of fish you can have.

It is a common myth that a smaller tank is easier to maintain and look after, but in fact, toxins and other harmful elements are diluted in larger bodies of water, making your fish less likely to become ill. So, if you are yet to buy your tank, it's actually better to buy the biggest one (within reason!) you can afford. If possible, do not buy an aquarium smaller than 25 litres, as it greatly limits the number and species of fish you can have. With such a small tank, a small shoal of tetras or a Betta fish would be about all you will be able to buy.

As a general guide, a tank between 25 and 100 litres is considered small, 100 litres to 200 litres is normally classed as medium, and a tank with a capacity of more than 200 litres is considered big. You can buy far bigger tanks than that for species and community tanks, but most beginners start off with something in the region of 100 litres.

It's very difficult to create an accurate formula with which you can stock your tank with the right number of fish, but there are several systems using number of inches of fish per gallon of water which are reasonable. This is a good website on the appropriate stocking levels of your aquarium, but my best advice would be not to rely on charts and tables, but join a forum and ask. When I first started fishkeeping, I knew nothing, so I asked hundreds of questions on various forums, and since the other members care about the wellbeing of the fish, they are generally very happy to help you.

Most fish you buy are not fully grown, and while most will not grow a huge deal more, it is well worth researching the adult size of fish so you don't get caught out. If you put a young fish in a small tank, it will become stunted and won't grow, but of course this is not good for the fish, so it's worth checking your fish aren't supposed to grow much more.

This one is too complex to explain in detail as I couldn't possibly list all the fish that often have compatibility issues, but it's something to look out for. While most fish you can buy in fish shops are good community fish that will live in harmony with one another, there are a few with an aggressive nature that will bully others, sometimes to death. I'm not trying to scaremonger, but do a little research before you buy the fish to check they will be compatible with the other fish in your tank.

Shoaling fish such as tetras and barbs should only be bought in groups of 6 or more. As well as feeling more secure as a group, a large shoal of fish always looks better than a few stragglers. So, if you have space, the more the better when it comes to shoaling fish.

Find out what the fish eats. If they are carnivorous ordinary flake food shall not be substantial, or indeed suitable, for them. If you feed your fish to a varied diet, they will be happier and their colours more vibrant, so every week give them small amounts of live (and frozen) bloodworms, brineshrimp and daphnia. Also, be aware that some fish will eat, or uproot, your plants in a matter of days.

This is more of a minor point, but still worth noting. If you are planning on buying fish with barbels, for example corydoras, make sure your substrate is either sand or round-edged gravel, and not anything sharp that could damage their sensitive barbels. I have read that even gravel is bad for them, but from personal experience, as long as it's not sharp, they will be fine, and mine even bred in my tank, so they were clearly very happy.

Thank you for reading my lens - I hope it gave you a few tips to think about. Please leave a comment if liked it or think there's something I could add.