How big a tank for 21 fish?

[D0c]

I currently have a 130 Litre, 42cm(h) x 90cm(w) x 36cm(d), tank.
I have one Goldfish roughly the size of my fist, 5 Zebra Danios and 1 Cory.

The goldfish was mine until I rehomed her when moving state and I've recently been able to get her back which is amazing, she's almost 3 years old and perfectly healthy apart from some swim bladder issues which are being maintained with sinking food.

Now the Cory I didn't know I was getting until I was picking up the goldfish, the person who had taken the goldfish bought the cory but gave him to me when giving me my fish back.

I have recently learned that Cories should be kept in schools.
Once I get through the hiring process at my new job and start getting money again I'd love to upgrade the tank to be able to fit a good school of cories and add some more danios.
I've been told a school of 10 each would be good.

What size tank would I need to comfortably house 10 cory, 10 danios and 1 goldfish?
I'm looking at 300 litres but i'm second guessing myself here haha.

 

[Aiken Drum]

From a bioload PoV your tank is big enough for those fish. My only concern would be filtration for the goldfish. Goldfish are messy and need a lot of filtration. When the fish gets to adult size it may need a filter rated for double your aquarium size

From a compatibility PoV there are issues. Goldfish are temperate water fish, corys tropical water fish. Finding a temperature that suits both will be difficult. Also as the goldfish gets to adult size it will try to eat fish small enough to fit in its mouth. Danios are agile enough to avoid this, corys less so. Corys also have barbs in their pectoral and dorsal fins, if the goldfish decides to make a snack of a cory the cory could get stuck in the goldfishes mouth and you would need to resort to cutting it out or lose both the fish.

Leave the goldfish in the 130 litre tank and get another tank if you want to keep tropical fish.

 

[D0c]

For filtration I've got a nautilus doing 1100 L/h. I overcompensated on that end haha.

Yeah the water temp side of it I have my heater on about 22C which I've been told is ok for goldfish. I read that Peppered Cories specifically are ok at temps as low as 20C.
I do want to keep my current tank as well though, so I could really move the cory into the new one once I get it.

 

[Aiken Drum]

22c is really a middle ground for goldfish and corys. Its a bit too warm for goldfish, too cold for corys.

They will both survive, but with issues. The goldfish for instance will increase its metabolism, more food intake, more waste etc. The opposite for the cory. You will likely see more cases of infection because their immune system won't be tip-top, and it will be more difficult for the fish to recover from these infections.

People do keep goldfish and corys together and they do it how you have suggested. I couldn't recommend it though and need to point out the issues.

 

[ColdKoi]

I mean I can’t say it’s a good idea, but in the summer it gets near 30c in my place. Water temps would typically be in the 28c range for a few months this summer!

The comets I’m growing out before they go outdoors didn’t seem to mind it one bit. It may have actually helped me a bit as I’m just trying to bulk them up but none the less they were just fine in water temperatures that high

Like mentioned, it’s likely more of a concern with the corys health but I’m sure you can find a happy medium there where both are happy. Even if it makes the poop factories increase production a bit lol

 

[flitabout]

Well minimum size tank for a goldfish is 30g or 113L, beyond that you will have temperature and filtration issues. You will need 2-3gallon per inch for adult size on a goldfish, Which roughly translates to 25 cm and that is just for the goldfish.

 

[D0c]

I'd really love to get a 300 litre or bigger, move the danios and the goldfish into that and decrease the temperature. Then keep the pleco in the 130 and add some more to make a school as well as increase the temperature for it.

I'm starting work on Tuesday so I'll have an income but my car won't tow a trailer and the only option is pick up a 300 litre tank from the city about an hour away (which I can't do with my car) or a bigger tank 120x60x60cm (which I would LOVE) but that's in the next state over and I can't get it delivered.

finding tanks while being far from the city is a real pain