Stocking 20 Gallon tank. HELP!

I have a cycled 20gal tank (600x 320 x 400

I made the mistake of trying to give my Betta (Sushi) some friends... he didn’t play nice to say the least. He now has his own 5 gallon set up and is very happy.

I have 2 Albino Cory’s - one with no eyes (Stevie Wonder) and one has 1 eye (Mike Wazowski) and I would love some stocking ideas as I’m new but a fast learner.

Lots of you will probably say I don’t have enough Cory’s for their school (the lady at the shop said a pair was fine) I intend of on getting some more. Do they need to be the exact same to school?

The fishies I am most drawn to are...

Neon guppies

Cory’s

Peppered catfish

loaches

tetras

Gold sucking catfish (Im pretty sure this would get too big for my 20 gal tank)

dwarf gourami

Our municipal water is
GH is 56 mg/L
PH 7.5

P.S my visually impaired Cory’s are doing great and are not letting their disability hold them back. I can’t be sure Sushi did take their eyes, I notice the eyes missing within an hour of getting them home and Sushi was too busy hunting the neon tetras to bother the Cory’s. The pet store offered to swap them but I was kinda fond of the little guys.

Eagerly awaiting suggestions of species and numbers! Thanks

You have learned the Betta rule that I repeat over and over on here and some refuse to accept, that male Bettas are not community fish. Now he is on his own, he will be very happy. He was attacking other fish because he was frustrated at their presence in his space, and that was extremely stressful to the Betta as well as those under attack. But that is now resolved to his pleasure to be sure.

To the questions. You have soft water so the fish mentioned (with the exception of the neon guppy) are good as far as the water parameters. If the neon guppy is in fact a guppy (there are "neon" colour guppies now) then it requires harder water to be healthy. Avoid any livebearer (guppy, Endler, platy, molly, swordtail). Neon tetras are softer water fish and fine here--and by the way, neons are almost always attacked by Bettas probably due to the bright colour.

Cories, yes, another three at least, or four is critical. The advice from the store was as wrong as it could be, which is sadly not at all uncommon. A group of five is minimum, with more if tank space3 allows, as this is a very social fish and the more there are the happier and healthier they will be. You can mix species if you prefer; in my experience over 25 years with some 15 or more cory species, they don't seem to care as much about having their own species if there is a decent sized group. But it is usually best to acquire a few of the species, so here I would say you cold add 3-4 of another species for variety. The 20g tank will limit fish but this is fine.

I would avoid the dwarf gourami. Unless you obtain fish direct from a breeder, there is the risk of the fish carrying the iridovirus. If you like this gourami, a very close similar species is the Honey Gourami. One male and two females would be OK here as far as space, provided you have floating plants.

I need to know the exact catfish species to advise so I'll leave those. Same for the loaches...but here all will be too large for this tank with the exception of the kuhlii loach, but not with cories.

Tetras...several of the smaller species will work here. These are all shoaling species, so a group of at least six but a few more is again always better for the fish, and your enjoyment of their interactions. There are some "nano" species like the Ember Tetra, or the Dwarf Rasbora in the Boraras genus, that work too. Some of the tetras can get nippy, some larger than will work here, some are more active swimmers so need longer tanks...but there are many less active and peaceful species. Neon tetra, glowlight tetra, cardinal tetra, Loreto Tetra...and many more.

Before I can suggest definite numbers, other than what I've mentioned above about the cories and tetras needing a group of each species, we need to pin down the intended fish a bit more.

Wow thank you so much for the very detailed answer.

It’s a real shame about the guppy! They are so pretty.

Can I split the Tetras like I can with the cory’s. Eg a few neon tetras and a few glowlight? I also like the long fun black widow. Sooo many choices to make.

What I would like to achieve is a bit of variety in the community but I also want to make sure the fish are happy and healthy.

Should I add each species after the other or add them together?

I have attached some images to help with what I’m looking at.

starting with my 2 Cory’s
Could I go with..

2x Julii
2x peppered
3x neon tetra or glo
3x Keri tetra
2x long fin black widow tetra
1x honey gourami (or dwarf from a breeder)

That would be 15 fish total. Is that too many? For once they are fully grown??

Ok so I did the math and based on 1” per gallon (at max size) I think I could have...

7cm. 2x albino Cory

5cm. 2x Julii

7cm. 2x peppered

4cm. 3x neon tetra or glolite

4cm. 3x Kerri tetra or lemon tetra

5.5cm. 1x honey gourami (or dwarf from a breeder)

Any feedback on this is welcome.

And still the same question. Should I introduce them slowly or all together or each species at a time?

Cluelessone said:

Can I split the Tetras like I can with the cory’s. Eg a few neon tetras and a few glowlight? I also like the long fun black widow. Sooo many choices to make.

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With a very few exceptions, shoaling fish need a group of their own species to avoid problems, stress and worse; in insufficient numbers they can become aggressive, even peaceful species. This shoaling need is programmed into their DNA. When these fish are available in stores, they are generally juvenile or even fry; it is even more crucial for their healthy development that they have a group of their own. As fish age, and individuals die off, we can be left with one, two, three of a species. Sometimes even this causes problems, but often it is best to just let it/them live out their days in the surroundings they have become accustomed to. Depending upon the species, a group of seven or eight may be best; with the nano fish like the Ember, it need to be more, maybe 9-12. Considering just the neons and glowlights since you mention then, in a 20g I would aim for 7-8 of each.

Forget the Black Widow, long-fin or not. This tetra gets largish, and it needs more space or it can become very aggressive at fin nipping each other and other species.

Cluelessone said:

I have attached some images to help with what I’m looking at.

starting with my 2 Cory’s
Could I go with..

2x Julii
2x peppered
3x neon tetra or glo
3x Keri tetra
2x long fin black widow tetra
1x honey gourami (or dwarf from a breeder)

That would be 15 fish total. Is that too many? For once they are fully grown??

Click to expand...

It is not too many, it is actually not enough. But there are species unsuited to this small a tank. I already disqualified the Black Widows (they would need at least 8-9 in a tank with a length of at least 75 cm but preferably 90 cm). The Keri tetra needs 7-9 and being quite active, not suited to a 20g.

The cories are OK, six in total, with two of each of the three species. Honey gourami OK; I doubt you will find a breeder for the dwarf, depending where you are.

Neons and glowlights, 7-8 of each, no fewer.

Cluelessone said:

Should I add each species after the other or add them together?

Click to expand...

Always add all of each species at the same time, meaning all 7 or 8 neons together, and all 7 or 8 glowlights together, and all six cories together (or the four new ones together with the two already there). Shoaling fish will always settle in faster with less risk of ich and other stress-related issues the more there are.

Beyond that, you don't want to overload the system with too many fish at once, but if you have live plants this is next to impossible to do so you are better there. But one species at a time is still fine. When I go hunting for new fish I can come home with 30-40 fish of different species, and they all go in my 20g quarantine tank for a few weeks; it is planted and runs permanently. But the point is that with floating plants you will never have cycling issues adding fish; you would have to be way over the tank's limit and groups of 12 or so tetras will never result in this occurring with floating plants. And you should have floating plants in with all of these fish, they will be less stressed (fish do not appreciate bright-ish overhead lighting and they will also be more colourful with some shade).

Cluelessone said:

Ok so I did the math and based on 1” per gallon (at max size) I think I could have...

7cm. 2x albino Cory

5cm. 2x Julii

7cm. 2x peppered

4cm. 3x neon tetra or glolite

4cm. 3x Kerri tetra or lemon tetra

5.5cm. 1x honey gourami (or dwarf from a breeder)

Any feedback on this is welcome.

And still the same question. Should I introduce them slowly or all together or each species at a time?

Click to expand...

I think I answered most of this in my previous post, but your mention of the inch per gallon needs a response. This is a guide that is fraught with difficulties to the point that it is useless and even dangerous. After all, you could keep 10 1-inch fish in a 10g perhaps, but not a 10-inch fish in a 10g, yet the "rule" applies to both equally.

There are many factors involved with numbers of fish in the tank. I discussed the need for a decent sized group, and the fact is that when you have fewer it is actually more of an impact on the biological system because the fish are now having troubles they would not have with a larger group where they can be more "relaxed" and "happier." The other species impact this too. And the aquascape, which must provide something close to what the fish "expect" like their own natural habitat.

That has been excellent! Your fishy knowledge is amazing.

First I will up my Cory population then I’ll go for at least 8 neon tetras.

The gourami I will leave until I can find a breeder, I know a few I can contact.

Black widow is out. Agreed

I’ll check these guys are all happy for a few weeks then add another group of glows

I think that will be enough in a 20gal. Once that settled I can reassess?

Cluelessone said:

That has been excellent! Your fishy knowledge is amazing.

First I will up my Cory population then I’ll go for at least 8 neon tetras.

The gourami I will leave until I can find a breeder, I know a few I can contact.

Black widow is out. Agreed

I’ll check these guys are all happy for a few weeks then add another group of glows

I think that will be enough in a 20gal. Once that settled I can reassess?

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Yes, this seems OK. Some upper level fish might be good, as everything mentioned is lower-half of the water column, so keep that in mind.

Byron said:

Yes, this seems OK. Some upper level fish might be good, as everything mentioned is lower-half of the water column, so keep that in mind.

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What would you recommend?

Byron said:

Yes, this seems OK. Some upper level fish might be good, as everything mentioned is lower-half of the water column, so keep that in mind.

Click to expand...

What would you suggest for the upper level fish?

Cluelessone said:

What would you suggest for the upper level fish?

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Given the soft water and keeping in mind the tank space being limited, again we are looking at more sedate (as opposed to active swimming) fish. Two of my favourites are hatchetfish and one of the pencilfish that swims at an oblique angle. Both will remain at or very close to the surface.

The hatchetfish species in Carnegiella are the smallest of the family and the Marble (Carnegiella strigata) is available more frequently depending where you live. A group of at least seven, but eight or even nine would be better. Floating plants but with open water as these do remain right at the surface. This genus is quite sedate, but when they are happy they will interact with each other. Another species in the same genus, Carnegiella marthae, is sometimes seen; plainer, but otherwise much the same. You can mix the two, though here space will limit this as you want sufficient of each species so they will not be stressed. The smallest of the known hatchetfishes is Carnegiella myersi, but this is a very delicate and sensitive fish and I would recommend the other two, especially the Marble, first.

The pencilfish is the Rocket or Diptail, Nannostomus eques. A group of 8 to 9 here. Floating plants, or at least plants reaching the surface, are mandatory. Make sure you keep the tank covered, these fish will jump (so will many others for that matter).

Thank you again! I need to have a really good think about what I want in my tank. I’m thinking now just 3 types a low a mid and a top because they all seem to be shoaling fish. Maybe Cory’s a type of tetra and hatchet fish?

I’ll have a dig and see what I can find nearby.

Thank you again!