20 Gallon Tank Questions about fish and stocking...

Aysu

Member
Hi all,

I’m very new to the aquarium scene, and while I am greatly enjoying it so far, I have a lot of questions that seem to have conflicting answers depending on where I look and who I talk to. I’ve been trying to do research online, but I’ve already made some boneheaded mistakes, though thankfully no catastrophic ones. My lesson has been learned about boiling driftwood before adding it to a tank.

I have a twenty gallon tank freshwater tank that I believe (fingers crossed) is now properly cycled. It isn’t much to look at, yet, but I’m pretty proud of it. It's about 4 weeks old with live java moss spreading across my driftwood tree, and a java fern happily growing (I just pulled a new fern off the original and weighted it to the substrate!). I'll probably transplant some dwarf hair grass from my mom's tank once hers spreads a little more. I've been doing tests every 2-3 days, and the chemicals all seem in balance even after stocking a few hardy fish, with the ammonia and nitrite holding at 0 mg/L, and the nitrate roughly at 5-10mg/L. I do weekly water changes of about 20%. I haven’t vacuumed the gravel yet because I read that it's important to let the bacteria get established in it, but I plan to do that once a month or so.

Currently, I have 3 zebra danios and 2 corydora catfish. I didn't realize that both zebras and cories should be in a school of at least 5 or 6, but the zebras seem happy swimming around the tank, darting in and out of the driftwood and fern, and across the tank and back. They aren’t keeping each other from eating, they aren’t harassing each other or the cories, and I have seen no signs of aggression, stress, or biting; the only odd thing is that they only school if I’ve been sticking my arm in the water to adjust the plants. I read that it's common for zebras to not school if there are no predators in the tank, which makes sense, but some confirmation would be appreciated.

The 2 cories are newer additions, only a few days in the tank, but they don’t seem to be distressed either. They just follow each other around the tank, chill under the driftwood, and dig in the substrate for food. I’d like to get a couple more anyway, because they are really neat to watch school (or is it shoal?), but I'd also like to add a third kind of fish.

So now comes the oft-asked question: how many fish can I add/have? I’d like to add a school of neon tetras because I love their colors. However, I also want to make sure my fish are happy and healthy. The general rule of thumb is, of course, one inch of fish to each gallon, but I’ve seen a lot of people saying it's perfectly fine to have more, if proper water changes are done regularly. My original plan was 3 zebra danios, 2 Cory catfish, and 6-7 neon tetras.

The employees at the local fish store I’ve been buying my equipment and fish from (not petco, no worries), said I could easily stock 12-20 neons in my tank, and assure me that neons, zebras, and cories do well together, and that my stocking idea should be fine for my tank. They have a large number of beautiful and healthy tanks in the store, both planted and not, and seem knowledgeable about aquariums, with more concern towards the health of a tank, rather than closing a sale. However, after doing more research on my own, I’m worried about the small school sizes.

Ideally, I’d like to have all three kinds of fish in proper school sizes (5 danios, 3 corydora, 6 tetra) but I worry that that would be too many fish for a 20 gal aquarium. Can I stock that many fish in my tank? Do I even have the right numbers for the fish? Am I overthinking the school sizes and stocking since the fish are happy with the smaller number? What would be a good number of each of these fish?

I've attached an image of my tank from yesterday. There's a bit of a bacteria bloom from adding the two cories, but water parameters are still good today.

Thank you for your help!
 

Ghelfaire

Member
Danios will school when you have 6+. If you don't want more zebras you can add leopard danios, same fish different pattern.

Corydoras feel safer in groups, they'll stick together but not necessarily school.

Don't add their 15-20 neons, you could probably get away with 6. If you overstock your tank you have to do larger water changes.
 
  • Thread Starter

Aysu

Member
Ghelfaire said:
Danios will school when you have 6+. If you don't want more zebras you can add leopard danios, same fish different pattern.

Corydoras feel safer in groups, they'll stick together but not necessarily school.

Don't add their 15-20 neons, you could probably get away with 6. If you overstock your tank you have to do larger water changes.
Thank you for the fast reply!

I wasn’t planning to add that many neons, don’t worry! I don’t mind adding more zebras—I'm fond of them from when I had a few as a kid—but if I add 3 more, can I still add the 6 tetras? Or would that overstock the tank? And should I get another cory, and if so would that be over stocking? I don’t mind doing larger water changes; it isn’t difficult, and time isn’t a concern right now in my life.

It probably shows, but I’m a little nervous because I’m so new to actual aquarium keeping. There's a lot more to it than I thought.
 

Ghelfaire

Member
The neons are tiny and have a small bioload, 6 should be fine.
Do you know what species of corydora you have? That'll also help to know.
 
  • Thread Starter

Aysu

Member
Ghelfaire said:
The neons are tiny and have a small bioload, 6 should be fine.
Do you know what species of corydora you have? That'll also help to know.
I think they’re Corydoras atropersonatus?
 

FishGirl115

Member
You're understocked rn. You could definitely do 6 neons, 6 corys, and 6 danios. I would do this so they all have proper schools
 

candiedragon

Member
Technically most fish in the hobby are shoaling fish. Definitely raise your cory and danio groups up to 6, and I feel like you could do up to 10 neon tetras and that would be just about fully stocked. I think a good 30% weekly water change would be okay, but once you get fully stocked just make sure to keep track of your parameters and adjust your water changes accordingly. Just my .02
 
  • Thread Starter

Aysu

Member
FishGirl115 said:
You're understocked rn. You could definitely do 6 neons, 6 corys, and 6 danios. I would do this so they all have proper schools
Good to know I can do proper schools for all of them! I know I'm understocked right now because I’ve been slow about introducing the fish, so that the bacteria has a chance to catch up.

I must've been underestimating how many fish my tank can hold. I’ll definitely get the groups up to the right numbers for each kind. It might be hard to find the same cory as the two I already have. I’m not sure what kind they are. I thought maybe they're Corydoras atropersonatus, but after looking more closely at the spot pattern on theif tails, I’m not so sure.

Anyway, thank you for your help!
 

candiedragon

Member
Maybe corydoras schwartzi?
 
  • Thread Starter

Aysu

Member
candiedragon said:
Maybe corydoras schwartzi?
I think that's it. They look identical to a google search, anyway. Awesome, thanks!
 

Noroomforshoe

Member
I would do 8 zebras, 6 cories, and possibly a non-schooling fish, but I would not keep 3 schools in a 20.
 

candiedragon

Member
Noroomforshoe said:
I would do 8 zebras, 6 cories, and possibly a non-schooling fish, but I would not keep 3 schools in a 20.
It's actually pretty balanced if you think about it. Danios typically stick near the surface, most corys stick to the substrate, and neon tetras generally take up the middle column.
 

Noroomforshoe

Member
Its still too many fish IMHO
 

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