Can a big tank over-stress a betta?

I hope I don’t sound stupid, but I’ve had two betta fish and both died within three days of owning them.
I’ve owned fish before, I understand how to cycle a tank before ever buying fish to put inside. But with the bettas, this is what happened: My tank (an Aqueon 20 with heater and filter and fresh plants) was cycled using a couple of frozen brine shrimp every day for over a month. When my tank was fully cycled I wanted to add just a betta. The tank was planted and I thought it was pretty enough not to need a lot of fish. The night I got my first betta home I gradually introduced him to the tank, first letting him adjust in his cup to the water temp, then gradually adding a little of my tank water at a time to his cup, then finally letting him swim free in the tank. He was dead when I woke in the morning. The store did an exchange. But the second betta died three days after I brought him home (I had been carefully testing the water each day). The store insists that a twenty gallon was too big for a betta and the stress of the space killed it. I put a school of rummy nose tetras in there and they are thriving years later.

Is the store correct? I am thinking of planting a 29 gallon, and my dream is still to have a planted tank with just a splash of color and life that a betta can provide. I think that would be beautiful. But not if it will kill another fish. However, I’ve never heard of a space being too big for a fish. Is this a thing?

I hope I don’t sound stupid, but I’ve had two betta fish and both died within three days of owning them.
I’ve owned fish before, I understand how to cycle a tank before ever buying fish to put inside. But with the bettas, this is what happened: My tank (an Aqueon 20 with heater and filter and fresh plants) was cycled using a couple of frozen brine shrimp every day for over a month. When my tank was fully cycled I wanted to add just a betta. The tank was planted and I thought it was pretty enough not to need a lot of fish. The night I got my first betta home I gradually introduced him to the tank, first letting him adjust in his cup to the water temp, then gradually adding a little of my tank water at a time to his cup, then finally letting him swim free in the tank. He was dead when I woke in the morning. The store did an exchange. But the second betta died three days after I brought him home (I had been carefully testing the water each day). The store insists that a twenty gallon was too big for a betta and the stress of the space killed it. I put a school of rummy nose tetras in there and they are thriving years later.

Is the store correct? I am thinking of planting a 29 gallon, and my dream is still to have a planted tank with just a splash of color and life that a betta can provide. I think that would be beautiful. But not if it will kill another fish. However, I’ve never heard of a space being too big for a fish. Is this a thing?

I should add that my plants were all very hardy, so I only added one or two root tabs, no additional plant chemicals, and all the plants had been in there before I even started the process of cycling.

 

I don't think that's true. In the wild bettas have more than 20 gallons of swimming room. I have a betta in a 36 gallon tank and she's fine. I also have a betta in a 5 gallon and tbh the betta in the 36 is bigger and more active.If the tank is really tall that will be a problem bit otherwise it's fine.

 

I don't think that's true. In the wild bettas have more than 20 gallons of swimming room. I have a betta in a 36 gallon tank and she's fine. I also have a betta in a 5 gallon and tbh the betta in the 36 is bigger and more active.If the tank is really tall that will be a problem bit otherwise it's fine.

The tank is wider than it is tall. It is 20” tall. Should I try to find one that is wider but shorter than that?

 

If the tank is large, many fish species, including bettas, will try to find an area they can call home. That becomes their territory. Make sure there a suitable areas where the betta can feel at home.

 

I don't buy it. That may be true in a bare-bones set up, but not in a planted tank.

You can never have too many plants.

 

I'd suggest not getting any info from this store.

Unfortunately Bettas are a species that have wishy washy genes due to incessant breeding. I find it to be very rare that a keeper of Bettas never had to treat all of their Bettas at least once. Usually no fault of the keeper.

We've drip acclimated and float acclimated our Bettas. Sometimes even exercising extreme caution does nil towards the genetics or store care. We have gone to only purchasing Bettas from stores/breeders that keep them in minimum 2.5gallon tanks. For whatever reason those cup prisons always produce problems.

 

We have gone to only purchasing Bettas from stores/breeders that keep them in minimum 2.5gallon tanks. For whatever reason those cup prisons always produce prproblems

The tank is wider than it is tall. It is 20” tall. Should I try to find one that is wider but shorter than that?

Is it a short finned betta I think you would be fine even a long finned betta would be fine but the longer fins make it harder to swim I've noticed. Like what keeperofanno said try and buy bettas with decent care conditions(maybe rule out petco/petsmart unless the betta cups are really clean) if your looking online for somthing I like Mbs bettas and bobstropical fish but they can be pricey.

 

Did you put in stress coat when adding (up to a couple days after adding)?

I think it is possible a fish got stressed due to new, large habitat. Yes, in the wild they get more than 20 gallons, but these bettas aren't wild, they spend their whole lives in the store until getting adopted. They're more fragile then us humans.

I would try a 3rd time. & then give up on it if it doesn't work. Try one more time. May've just been bad luck / sick fish.

How did they do when you put them in? Were they swimming good? Exploring? Eating? Or did they just go to the bottom & sit?

 

That’s a good call on getting them from better stores. There is a specialty fish store that I can go to not too far from here. The two I got were from Petco. They seemed to swim just fine, but they both just sat in the leaves-no exploring around.

 

If the tank is really tall that will be a problem bit otherwise it's fine.

Even in that case I doubt there is many home aquariums that would be tall enough that it would be an issue.

That’s a good call on getting them from better stores. There is a specialty fish store that I can go to not too far from here. The two I got were from Petco. They seemed to swim just fine, but they both just sat in the leaves-no exploring around.

I would also suggest a different store.

 

I've had them in a 125 planted. When I first put them in they are kid of freaked about having so much space, After all, they've been in nothing but a little cup all their life. After a few days they start exploring around. It doesn't take long until they are happy with all the space.

 

No way, a 20g is in no way shape or form too big for a betta. I previously had a betta living in a 125g community tank and he THRIVED. There is such thing as too big of tank for individual bettas. They like to breathe air on the top of the water and the really heavily finned ones like over exaggerated dumbo halfmoons and such sometimes the fish struggles to swim because the fins are so heavy. That's a big reason why I recommend against the crazy large finage.

I'd say either something was going on with the fish honestly. Maybe they were really old or if they lived in cups for a long period of time sometimes they don't have the muscle to handle a bigger tank right away.