When you're staring down a tank of green water, purchasing one of those cute little Chinese algae eaters may seem like an easy way to clear things up for your shiny goldfish friends. It's not. There are several reasons why a Chinese algae eater and goldfish won't be best buds.
What Is This Stuff, Anyway?
There are a few different kinds of algae. Some, the oxygenating plants, you want in your tank. Others, the green water kind and various-colored slimes, not so much. Green water algae, also known as cyanobacteria or blue-green algae, isn't really a plant at all. Neither are the multifarious slimes—most of these are protozoa, not plants. Very few of them are actually nutritious for "algae-eating" animals, which need to be fed real plants to thrive, such as aquarium plants, romaine lettuce, cucumber, frozen or wafer plant-based fish foods...you get the idea.
Bring On the Slime!
Young Chinese algae eaters, however, do actually eat the aforementioned slime. Sounds great, right? Wrong! As they grow, they become more carnivorous, but keep their taste for slime, and the sides of your goldfish start to look like the perfect snack. Older, larger and more dangerous algae eaters will attach themselves to more defenseless fish, and goldfish are some of the most peaceable and slimiest tank mates they could imagine—altogether a bad mix for you, the fishy pet owner.
Older Chinese algae eaters are also very territorial. Like their so-called algae-eating cousins, the plecostomus ("sucker fish"), they don't even really like their own kind. All bets are off when it comes to other species, especially gregarious, nosy species like goldfish, which like to swim in groups and check stuff out, and who do not understand the concept of personal space.
Hey! Where're We Going?
When it comes to your fish tank, size does matter. Unfortunately for those tiny little Chinese algae eaters in the store, they do not stay small enough to fit in most living room tanks as adults. These guys measure almost a foot long at adulthood —which means that most of them get evicted when their tank can no longer hold them—unpleasant for you and very unfair to your swimming pet. The bottom line is, do not purchase these fish unless you have a very large tank and want only one or two fish inside it. Definitely do not buy one to mix with your goldfish.