Glofish Tetras being a little aggressive

[Kinz]

Hello! I got a 15 gallon tank not too long ago and currently have 4 cory cats and 5 Glofish tetras in it. I planned on getting another cory so they’d have a little school, but my glos are being a little aggressive with each other. I don’t know if I should get another (or if I even have the room for that in a 15 gal), or if it’s because I have two with short fins and three with long? I was told they would still school, but at this point I don’t trust anything a pet store tells me haha.
My water levels are fine, as far as I can tell. Ph is around 7.9 so I’m working to lower that a tiny bit with peat, and Nitrates moved to 0, but that’s about all that seems possibly concerning. Everyone’s eating fine and behaving alright besides that!

 

[Colin_T]

Pictures of the tank and glowfish so we know what species they are?
What are the tank dimensions (length x width x height)?

 

[WhistlingBadger]

...at this point I don’t trust anything a pet store tells me haha.

Good, good. You've already learned one of the more valuable lessons in the hobby.

Sounds like a space/numbers issue to me. Do your fish look like this?

If so, you have genetically engineered black tetras, which can be fin-nippy in small numbers or in small tanks. Seriouslyfish (a good go-to source for species research) says that they should be kept in a school of at least 6-8 specimens, in at least a 70l (18g) tank. Crowding and low numbers are a combination that does tend to cause aggression. Read up on the species here.

Gymnocorymbus ternetzi – Black Widow Tetra — Seriously Fish

www.seriouslyfish.com

On the other hand, if they look like this

then you have genetically modified tiger barbs, which are mean little cusses unless kept in large numbers with lots of room. If this is what you have, I'd get a much bigger tank or rehome them.

Finally, there are these:

These are zebra danios, which are nice little guys but extremely active. They need a lot more space then their size would make you think because they're kind of hyperactive. I could see them being aggressive from sheer boredom in such a small tank, in such small numbers.

Hope that helps.

 

[Kinz]

Pictures of the tank and glowfish so we know what species they are?
What are the tank dimensions (length x width x height)?

Roughly 13 x 13 x 18.5 inches. It’s a tall tank rather than lengthy. I was mainly trying to get a better picture of both short and long finned haha.

 

[Kinz]

Good, good. You've already learned one of the more valuable lessons in the hobby.

Sounds like a space/numbers issue to me. Do your fish look like this?

If so, you have genetically engineered black tetras, which can be fin-nippy in small numbers or in small tanks. Seriouslyfish (a good go-to source for species research) says that they should be kept in a school of at least 6-8 specimens, in at least a 70l (18g) tank. Crowding and low numbers are a combination that does tend to cause aggression. Read up on the species here.

Gymnocorymbus ternetzi – Black Widow Tetra — Seriously Fish

www.seriouslyfish.com

On the other hand, if they look like this

then you have genetically modified tiger barbs, which are mean little cusses unless kept in large numbers with lots of room. If this is what you have, I'd get a much bigger tank or rehome them.

Finally, there are these:

These are zebra danios, which are nice little guys but extremely active. They need a lot more space then their size would make you think because they're kind of hyperactive. I could see them being aggressive from sheer boredom in such a small tank, in such small numbers.

Hope that helps.

Yeah, they’re tetras! One of each color except the red. I’ve always had a small 5 gal with some of them but wanted to get an upgrade. I’ve never heard that their limit was an 18 gal before! I definitely can’t size up unfortunately. Does that mean getting another would be a bad idea? It’d be nice if they wouldn’t nip at each other as much.

 

[WhistlingBadger]

A fifteen gallon tall is a very small tank for this species. "Floor space" (we usually call it footprint) is more important than height for most species. Black tetras really should have a 2' wide tank or so. That isn't an absolute rule, but it's good advice from seriouslyfish.com. I suspect that, with this little swimming space, you're going to keep having aggression issues. I would advise against getting another one. If I were in your situation, I would look to rehome these fish (will the pet store take them back?) and look for something more suitable to the tank I have.

I realize that's a bummer, and no one is trying to make you feel bad. Most of us have made similar mistakes when we were starting out.

 

[Kinz]

A fifteen gallon tall is a very small tank for this species. "Floor space" (we usually call it footprint) is more important than height for most species. Black tetras really should have a 2' wide tank or so. That isn't an absolute rule, but it's good advice from seriouslyfish.com. I suspect that, with this little swimming space, you're going to keep having aggression issues. I would advise against getting another one. If I were in your situation, I would look to rehome these fish (will the pet store take them back?) and look for something more suitable to the tank I have.

I realize that's a bummer, and no one is trying to make you feel bad. Most of us have made similar mistakes when we were starting out.

Ahh I was afraid of that. I’ve had four of them for about a month now, and the fifth one I’ve had for the entire quarantine, so at least two years. Kinda why I wanted to get an upgraded tank and more buds for him, cuz I couldn’t do anything for him for so long.
I did read that tall tanks weren’t as great, but it was AFTER I got one and before I did so much research on it. Idk if the store will take any back at this point, plus I’m gonna be stranded at home for at least 5 days anyway. Push comes to shove, I think our dentist office has a tank of em? If I really had to hand them off.

 

[Colin_T]

Can you get a bigger tank for them?
If you can, then just move the fish, gravel, plants, water and filter into the new tank.

 

[Kinz]

Can you get a bigger tank for them?
If you can, then just move the fish, gravel, plants, water and filter into the new tank.

Definitely not. Spent enough money on this one and on a stand for it, not to mention all the smaller stuff I didn’t realize I needed until afterward. As a college kid that’s about all I can afford. Pretty sure my mom would kill me if I said I needed a different one. Plus I don’t have the room for anything bigger.
I was originally just going to go up to a 10 gal lengthy tank, but y’know. Noob + Petco employee did not mix well. Though I suppose it’s good I didn’t get a 10 gal for the glofish at the very least.

 

[Byron]

I would not give these fish to anyone else to add to their tank (like the dentist). When fish have been impacted by environmental factors that cause stress (like the numbers of the species, and/or tank space), the stress alters the fish's behaviours and it is usually not reversible. The increased aggression was the fish's only response to the stress. It is a very different thing from a dog that misbehaves and can be taught not to repeat it.