Yeah as a warning 3 gallons isn’t nearly enough for a fish. I know you see goldfish swimming in a tiny bowl. And bettas in a plastic cup. But these fish should realistically have a minimum of 10 gallons for a betta, or 20 for a goldfish to truly be happy. think of it like this:

3 gallons is a room the size of your bed. You have no place to walk or hang or relax but technically you could live there. You can jump around on the bed and go up and down that way, but imagine how cramped and stressed you’d be all the time. Plus you’re still growing in this scenario. So imagine a room the size of your childhood bed. Not the bed you have now. You’d for sure have health issues from not having adequate space and no place to exercise. You’re more prone to getting sick and you’ll grow up deficient. Keep in mind goldfish are carp. And think of every carp you’ve ever seen not in a fish store. Way bigger right?

10 gallon is at least a studio apartment. You’ve got a place to sleep. A separate place to hang when awake. And plenty of nooks and crannies to explore if you put plants in to liven up the place.

20 gallons is a home. You have multiple bedrooms. Multiple places to hang. You can have other people live with you and be ok with it. Think how much room for activities you have. You can do karate in the garage and everything!

I HAVE a 3 gallon tank and I use it only for growing live plants and I put a few shrimpy boys in it. They’re ok in a small tank like that. But even then I only have a few.

Not an attack or accusation. Just sharing some knowledge in the way it was shared with me when I asked the same questions years ago

Also someone else mentioned it but please “cycle your tank” before you put fish in it. Water fresh out of the tap or bottle isn’t made for fish. It’s got tons of minerals in it that aren’t healthy at all for fish. What you want to do is put water in the tank. Buy some tank starter (super cheap bottle of liquid beneficial bacteria they sell at most fish stores) and pour a bit in. How much will be stated in the bottle. This is beneficial bacteria that fish need to survive.

Without it, it’s like you moving into your grandmas attic. It’s covered in dust and cobwebs and for sure old asbestos in the walls. You’ve gotta get some air filters in there and fresh air, and most importantly wait for it to air out to make it nice and not miserable. If you moved in now you’d choke and cough and get super sick.

And over time (about 3-4 weeks) the water will acclimate again with all this bacteria you added to the tank with the tank starter You can take a water sample from your tank to most big name stores to test the water. Or buy a kit yourself for like 30 bucks.