by Andy Gordon of England, and Michelle Stuart of Ontario Canada
Reprinted, with permission, from their web site Fishtanksandponds.net
Aquarticles

There are a good number of fish that have become established as good fish to keep in a community aquarium and with most of them that is the case. But there are some that a lot of books and dealers recommend as being fine but in fact they are poor subjects for the general community tank for varying reasons. Here is a "rogues list" of fish that should be treated with caution. This does not mean that all the following fishes can't be kept, because in the proper sized aquarium with suitable tank mates and conditions they all still have something to offer.

Angelfish
These fish are cichlids and grow quite large - 6 inches from top to bottom is not uncommon. Some can be quite aggressive with their tank mates. They have long flowing fins and are fairly slow moving, both of which make them an ideal target for fin nippers. And like most fish they regard any fish small enough to be eaten as potential food and it is quite common for neon tetras and similar fish to "disappear" when there is a large angel around.

Mollies (All types)
Are brackish water fish, which means they must have some salt in their water if they are to thrive. They are found only in coastal regions and even enter full saltwater occasionally. Without salt their health will suffer in the long term, and apart from salt they also require a high pH 7.8 to 8.4 and hard water. These are the conditions that DO NOT suit most other community fish, and because of this they should not be kept with other fish that require almost opposite water chemistry.

Sharks (Labeo sp.)
These fish are very quarrelsome, particularly with their own species or related species. They will also make a habit of chasing other fish almost non-stop. Although no actual physical harm is done (usually) any fish that is constantly being harassed will begin to show signs of stress.

Giant danios
Are fast enough, big enough and more than willing to eat smaller fish. Including lots of adult tetras.

Siamese fighters
In nature these are solitary fish. The males will fight on sight of another male and so will females occasionally. Even males and females only get together to spawn and regard each other as competitors the rest of the time. Most of the time other fish are left alone but like angelfish they often fall victim to fin nippers. Unlike most other fish on this list, if you want to keep them there are two rules:
1. Keep a single specimen and not a pair (unless you want to breed them, but even then they should be kept apart).
2. Choose tank mates very carefully and avoid any potential fin nippers

Tiger barbs
Are notorious for fin nipping. Tank mates must be robust and able to defend themselves in some way. Their behavior can be kept under control a little by keeping them in a shoal of at least 7 individuals; this tends to keep them busy squabbling amongst themselves. But angelfish, Siamese fighters and guppies or any other slow moving, long finned fish would still be targeted.

Plecs.
These fish are often sold as small young fish that will keep algae away from the tank by eating it. And for a while they will. But as they grow they become less interested in a vegetarian way of life and prefer a more balanced diet and will leave the algae to grow in preference to eating (and competing for) the more usual aquarium foods on offer. And despite what anyone tells you to the contrary these fish grow BIG - in excess of 12 inches, and they grow quickly too.

Harlequin rasboras
A surprise for most people to find these listed here? The reason being that their hardiness is very often over estimated. These are really quite delicate fish and they do require acidic, soft, high quality water conditions in order to thrive. They also require any tank mates to be reasonably quiet. If they are put in a tank with medium hard water, a pH of 7.2, nitrates in the mid 20s ppm (or above) and with boisterous tank mates (zebra danios) etc., they will live very short lives.

When starting a community tank it is a good idea to make a written selection of fish that have all been researched and that all:
1.Require the same water chemistry.
2.Are of a similar disposition. Very timid or gentle species shouldn't be kept with lively boisterous species, because they may lose out when competing for food
3.Whilst they don't all have to be the same size, you should generally avoid putting very large fish with small ones.
4.Don't under any circumstance impulse buy when it comes to fish. Always properly research the fish before you buy it. By research I don't mean asking the shop assistant - it is far better to read at least two good reliable books and get a realistic opinion about the species. Or better still. ask someone who has kept them.

Following these simple guidelines will help you build a community that is a pleasure to have, rather than one that goes from one problem to the next.

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