Danio erythromicron stowaway

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Aquarium Advice Apprentice
Feb 19, 2024
OK, so I have a heavily planted main tank (approx 25 US gallon) with 3 Glowlight danios (Celestichthys choprae) and I wanted to add more, so I bought a few more from pet shop and put them in my 7.5 gallon (ish) quarantine tank to QT them for a few weeks before I add them to the MT.

But there's an imposter! One of them is actually a Celestichthys erythromicron (dwarf emerald "rasbora" - close cousin of a CPD) that must have been housed in the same tank as the chopraes and got caught with them. It's tiny compared to the glowlights and so cute. I fell in love with it immediately (despite not deliberately trying to buy him/her) and now I'm having terrible multiple tank syndrome thoughts of setting up my empty 5.5 gallon as a species only tank and getting a few more of them.

Help! ?

In all seriousness though, can I keep a few of these micro danios in a 5.5 gallon? Has anyone successfully done this? I have a bowl with a bunch of guppy grass, and tons of excess moss in my MT, so I can put some of this into the 5.5 gal to make it cosy for them. I don't want to set up a larger tank if possible as I don't really have space for it, but the 5.5 gal is small enough to sit on my desk.

I really don't want to put the erythromicron in the main tank as there's also a rosy barb in there, and the danio is so small he may get eaten. Also the main tank's pH is always somewhere between 6.0 - 6.5 (big piece of driftwood, mature substrate, and lots of plants - I dont add anything to maintain this) and I read that these guys don't do well in acidic pH.

What would you do?
6 gallons is a little small. Im sure you can find someone who has kept those rasboras in such small tank and kept them alive, but it would be survive rather than thrive.

So its a decision on whats the best you can do with the fish. If you dont want to invest in a bigger tank, or maybe dont have the space, is it better to get a few friends and keep it in your 6g, or get a few friends and introduce them to your main tank, or return the fish and who knows what future?

Id be tempted to keep the fish in the small tank even though its less than ideal.

Can you use the 7.5g QT as a long term home? Thats a lot better than 6g.
"Can you use the 7.5g QT as a long term home? Thats a lot better than 6g."

The problem with the 7.5 gal tank is its really ugly and kind of weak. I was given it by a friend whose young son no longer wanted fish, and it's got a flimsy black plastic bottom (which seems fragile) and plastic rims down all 4 corners (I guess to hold it together?), I'm not sure if the sides are clear plastic or glass. It's the flimsiest tank I've ever seen and looks like it won't last long term filled with rocks and substrate etc, which is why I only use it temporarily as a bare bottom QT and then empty it afterwards.

If I put sand, rocks, plants etc in it I wouldn't be able to see if the seals are failing or the bottom is bending / cracking, and I don't trust the bottom of the tank with anything heavy on it.

But yes, I *could* go out and get a new sturdy 7.5 gallon tank (or maybe a 10 gallon if its more towards cube shaped rather than long) which would fit on the desk, or on a random piece of furniture somewhere. I really don't have space for a bigger tank requiring a stand though, at least until I've finished renovating the back room in my flat (needs new ceiling and plaster so it will be a while).

Would a 10 gallon be sufficient for a small group, perhaps with a few shrimp or snails as a substrate cleanup crew?
10g is usually considered the smallest tank for these fish. Its a fish ive never kept, but ive kept galaxy rasbora, and would be happy to keep a small group of those in a 10g tank with a couple of nerite snails or some cherry shrimp.
I have a problem with the C. choprae and the C. erythromicron - the dominant male choprae is intermittently chasing the other fish, including the little erythromicron.

I don't know if the male is trying to spawn again or if he's just a bully, but the poor little C. erythromicron isn't as fast as the C. choprae and is getting pushed around. I can't see any damage to him / her but it's causing him / her to hide, rapid gill, and look stressed. At least one of the other C. choprae is also occasionally hiding in the moss from the male choprae (doesn't look as stressed though since it's fast enough to avoid being bashed or nipped). I think I have 1 male and 3 females but it could be 1 dominant male, 1 smaller male, and 2 females.

Should I move the little erythromicron to another quarantine tank on its own? I'd have to clean and sterilise the 5.5 gallon tank and use that I suppose. Or I could move all of the choprae to a plastic storage box with larger dimensions than the current quarantine tank, and leave the little erythromicron where it is? The box would have to sit on the floor though which might be stressful for the fish when I walk around it to do maintenance on the tanks.

I don't have another seeded filter ready so whoever gets moved is going to have to survive possible ammonia/ nitrite fluctuations. I can add some live plants and some filter squeezings from the main tank but it likely won't cycle instantly and there will be some minor spikes.

Alternatively I could add more hiding places to the QT to allow the fish to hide better from the dominant male and keep them all in there, or I can put the D. choprae in my main tank early and risk disease.

What is the best course of action to keep everyone safe and happy?
These fish are social animals, and when kept in small numbers their behaviour becomes unpredictable. They may get overly aggressive, they might stop eating, they may hide away.

You mention adding a few more glowlight danios to a group of 3, but not how many danios you now have. It might be that more danios will keep any aggression within the group of the same species, it might not. The 2 fish species you mention are very similar, so it could be the larger fish establishing dominance over the smaller fish and adding more of the larger wont then change that dynamic.

If the smaller fish is being beat up, moving it is the best thing to do. Even though it might be stressful being on its own, that's going to be better than constantly living in fear of its tank mates.
The 3 original glowlights / choprae are in the main / display tank. None of them are aggressive with each other or any other fish (the only other fish currently with them is much larger so that could be why). I could only buy 3 at the time as they were the last 3 in the shop, the intention was always to increase the shoal size later on when they were back in stock.

I recently bought 4 more choprae to add to the original 3. These are in the quarantine tank. A fifth fish, a C. erythromicron was accidentally included in the bag by the store clerk, so I ended up with 1 lone C erythromicron (it must have been the last one left at the shop because I didn't notice them in the choprae tank). So I have 4 choprae and 1 erythromicron in quarantine and 3 choprae in my display tank.

I'm hoping that when I add the 4 new choprae to the display tank that they will all happily coexist. If it turns out they need an even bigger shoal, then hopefully the fry the new choprae created in the QT will grow into adults and they can also be added :)

I suppose I will clean and sterilise the 5.5 gallon tank tonight and set it up tomorrow for the little C erythromicron. If I can find more of them in another shop at the weekend, I'll get a few more so that its not lonely.
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