How To Select Fish For Aquarium

Pet stores are mostly selling you garbage.

I just got back from looking at a local shop’s tanks, and my head is pounding from seeing sick, dying animals. If you are confused about how to select fish for aquarium, you are basically just throwing your money into a watery grave.

It totally sucks. You see a bright orange thing darting around the glass and you immediately want it in your living room. But buying on impulse is the absolute fastest way to ruin your tank.

The absolute worst way on how to select fish for aquarium

Most beginners literally just point at the prettiest color. Wrong. You have to look at the other fish sharing that exact same water.

If there is a single dead fish rotting in the corner, walk away immediately. I don’t care if the one you want looks totally fine right now. They share the same filtration system, meaning they share the exact same microscopic nightmare pathogens Wikipedia/Ichthyophthirius multifiliis.

Parasites spread fast. Really fast. If you buy a supposedly healthy fish from a contaminated tank, you are just bringing a ticking time bomb home.

It blows my mind how many people ignore dead bodies in a display tank. They just point past the corpse and say, “I’ll take the blue one.” Idiots.

My biggest disaster as a beginner

Let me tell you about a horrible Saturday night back in March 2012. I bought this adorable, tiny little red-tailed catfish because it looked cute wiggle-swimming at the pet store. I dumped it right into my 30-gallon tank with a dozen neon tetras because I didn’t bother to research anything before driving to the store.

Two weeks later, every single tetra was missing. Gone. I woke up at 4 AM to a massive splashing sound and found this fat, rapidly growing monster catfish choking on my prized angelfish.

I felt so incredibly stupid and utterly ashamed of myself. I literally cried holding a net because I caused those fish to suffer simply because I bought an animal without understanding its adult size. Do your research.

Figuring out how to select fish for aquarium

You have to ask the store employee to feed the tank before you buy anything. If the fish doesn’t immediately attack the food like it hasn’t eaten in a solid week, leave it there. Healthy fish are always hungry.

Always hungry. A fish that ignores food or spits it back out is already dying. It is just a biological fact.

You also need to stare at their fins and skin. Closely. If the fins look ragged, clamped tightly against the body, or covered in tiny white salt-like dots, that fish is severely stressed out or actively infected with something nasty.

When thinking about how to select fish for aquarium, you have to consider the stomach shape. A healthy fish is nicely plump. If the belly looks pinched, sunken, or totally hollow, that animal has internal worms or has been starving for weeks in the wholesale distribution chain.

Do not buy the runt. Never buy the runt. People always feel sorry for the tiny, bullied fish hiding behind the filter tube and think they can save it.

You cannot save it. That fish is hiding because its immune system has totally crashed from severe social stress, and it will definitely die in your quarantine tank. Let someone else waste their money.

My highly unpopular opinion about tank mates

Here is something that makes people on forums absolutely furious with me every time I say it. Community tanks with six different species are complete trash and you shouldn’t build them. You just shouldn’t.

People treat their glass boxes like Noah’s Ark, buying two of every random species they see on a Sunday afternoon. It ends up looking like a chaotic, stressful clown car. Fish don’t want to live in a crowded subway station with a bunch of weird strangers darting around them all day.

Keep it simple. Pick one large school of tetras and maybe a single centerpiece fish, and stop treating the pet store like an all-you-can-eat buffet line. Your fish will live so much longer if they aren’t constantly stressed by weird, incompatible tank mates.

More tips on how to select fish for aquarium

Think about what level of the water the fish actually lives in naturally. Some fish are strict bottom dwellers like corydoras. Some strictly swim at the very top of the water column.

If you buy all top-dwelling fish, the bottom of your tank looks like a barren wasteland while the top is a crowded, hyperactive mess. Balance. You want harmony, not a traffic jam.

This is exactly why understanding how to select fish for aquarium matters so much. You want a bottom feeder, a mid-water school, and maybe a top swimmer. If you need a good net to safely move your new pets into their proper zones, Check out our fish care supplies here.

Stop trusting the labels

Store labels lie. Constantly. They will label a fish as “peaceful” when it is actually a notorious fin-nipper that will shred your fancy guppies into confetti while you sleep.

You have to know the species before you walk through those automatic doors. Pull out your phone and search for the adult size, diet, and temperament of whatever catches your eye. Never trust the teenage kid working the registers who just wants to make a quick sale and go on their lunch break.

Pay attention to how they are breathing because it tells you everything. Fast, heavy gill movement is a massive red flag. If a fish is gasping at the surface or its operculum is flapping a mile a minute, the water quality is absolute garbage.

You really need to think about water chemistry before bagging them up and driving home. Discus need soft, acidic water, while Rift Lake cichlids want liquid rock. If your tap water is extremely hard, do not buy soft water fish unless you want to mess with expensive reverse osmosis units for the rest of your life.

Do not ignore this basic chemistry rule. It breaks my heart when I see people forcing fish to live in the completely wrong pH just because they thought the fish looked pretty in the store. Brutal.

Learning how to select fish for aquarium takes real, frustrating patience. You will go to the store and leave empty-handed nine times out of ten. That is totally normal.

It means you are doing it right. You are waiting for the perfectly plump, active, aggressive eater that will actually survive the stressful car ride home. Trust your gut.

If a fish looks wrong, it is wrong. If the water is cloudy, walk away. Move on.