Pygmy Corys in Hard Water?

Alright, I've got a big piece of driftwood covered in biofilm in the tank. Too big, in fact; I'll keep it in until the otos are healthy and there's biofilm elsewhere and more stuff for it to grow on, but I probably won't keep that piece in the tank permanently because there's just no good place to put it among my other decorations. The otos seem happy, although they don't look much rounder immediately. They've never been lethargic/acting distressed tho, and they seem to be investigating more things in the tank. Could you send a picture of what their bellies are supposed to look like once they're healthy?

Side discussion: I won't be introducing anything new for a while, but do you have any suggestions for schooling fish (to replace the danios/WCMMs) that would be peaceful and not bother the cories? I was looking at emerald rasboras before the cory/oto saga, and descriptions say they're peaceful, but also that they are playful/active swimmers so I'm not sure if they would actually be better. I'm also interested if there's any danio/rasbora/tetra type fish that's a little smaller (like <1 in. rather than 1.5-2 in.)? Seeing the cories schooling together has made me realize that having a big school of tiny fish is more fun than the other way around.

JackGulley said:

Alright, I've got a big piece of driftwood covered in biofilm in the tank. Too big, in fact; I'll keep it in until the otos are healthy and there's biofilm elsewhere and more stuff for it to grow on, but I probably won't keep that piece in the tank permanently because there's just no good place to put it among my other decorations. The otos seem happy, although they don't look much rounder immediately. They've never been lethargic/acting distressed tho, and they seem to be investigating more things in the tank. Could you send a picture of what their bellies are supposed to look like once they're healthy?

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That's good! And yes, no need for it to be a permanent fixture, these are just emergency measures to try to save the otos. If you've borrowed the wood from someone's established tank, it'll also help to seed your tank with the biofilm, algae and microcritters that the otos survive on.

It's a good sign that they're still alive! My heart sank when I first saw I had a notification for this thread, expecting bad news, because it's so common for them to die within the first 24 hrs once someone has bought them home in poor condition.

These images show how a healthy oto tummy looks. Should be a proper rounded area of their tummy at all times, since they're continual grazers.


I've nicked these photos from articles since I don't have photos of my own fish on this new laptop. Bear in mind that as said before, there are different subspecies of "common" otos, which accounts for the visual differences you see here. For example, in my gang of eight otos, one is a tiny sub species, while another that I rescued from a neglected tank for sale is much larger than any of the others, and a sub-species I hadn't seen before, and he's 2-3 times the size of the smallest one.

In one of the photos you can see some redness of the gills on one of the fish. This is normal, it's only because the skin is thin there, so you're actually seeing the gills. Happens often in plecos, especially the albino and lemon colour mutations, so isn't anything to worry about if the fish is otherwise well, and not gasping. Red gills can be an indicator of a problem like gill flukes or toxic water, which is why I mention it, but if your otos have red gills, aren't gasping, and othewise seem okay, then don't worry about it.

It's good that they're actively investigating the tank. They'll be looking for food, so it's a good sign that they still have the strength and motivation to search for food.

Doesn't mean they're out of danger yet, but it's good that you've got the driftwood, and that you care and are doing what you can for the little fellas. I'm pulling for them, and for you!

While looking for decent photos of oto bellies, one of the articles I pinched a pic from gives a lot more detail about otocinclus and their needs. I haven't read the whole thing, only scanned some parts, but from what I've seen so far, it looks accurate and helpful:


It includes something I've known about but didn't mention before because it's horrible... but the people catching otos often use a poison like cyanide to stun the school of otos, bring them to the surface and makes them easier to catch. Once you know what otos go through before landing up in our home tanks, it makes it easier to understand how delicate they are, what they've already been through, and why we urge so many precautions for getting these adorable and useful little fish. Forewarned is forearmed, and now you know, hopefully these two will make it, and you'll be better prepared for when you're ready to get more.

JackGulley said:

Side discussion: I won't be introducing anything new for a while, but do you have any suggestions for schooling fish (to replace the danios/WCMMs) that would be peaceful and not bother the cories?

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Oh yes, there are lots of options! So so many that you're spoiled for choice. Especially given the following things you said...

JackGulley said:

I was looking at emerald rasboras before the cory/oto saga, and descriptions say they're peaceful, but also that they are playful/active swimmers so I'm not sure if they would actually be better.

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They definitely would be better! There are the emerald rasbora, and their close relation, the celestial pearl danio, or you could consider fish like ember tetra, chili rasbora, green neon tetra, kubatoi rasbora... there are so many options! Look at what's termed "nano fish", and "nano tanks". A 20g long gives you a huge amount of options, and those fish are active and swim around, but won't outcompete or scare the pygmy cories the way a group of zebra danios and WCMMs do.

The pygmies don't mind active swimmers or shoaling fish like the above mentioned, they enjoy the activity in fact! They'll often join in the group when they're in the mood, and when they pop up to the surface for a gasp of air. They're shy and more withdrawn if the upper level fish are much larger, more aggressive, or are at risk if the upper layer fish are voracious eaters, like the zebra danios, so they get outcompeted for food.

But you can still have peaceful, colourful, active and fun to watch large groups of small fish like the ones above, and in a big group like a school of 20 pygmies, 6 otos and a group of 12 ember tetra and 12 celestial pearl danios for example, you could manage that in a 20g long once it's well established, if it's also well filtered and well planted, and you do the weekly maintenance, and make sure you have the right tiny foods for these fish! It's very do-able.
Some frozen foods like cyclops and daphnia, whether live cultured or frozen, are especially good, because they float like a cloud in the water column, allowing all the fish to get a chance to eat. They're often used for feeding fry for the same reason, and for their small size. Since pygmies and most of the species mentioned above have tiny mouths, the food needs to be tiny. I've used a pestle and mortar to crush dried food into smaller pieces, until a friend recommended getting a pepper mill, now I can just grind the Bug Bites microgranules even smaller straight into the tank.

JackGulley said:

I'm also interested if there's any danio/rasbora/tetra type fish that's a little smaller (like <1 in. rather than 1.5-2 in.)? Seeing the cories schooling together has made me realize that having a big school of tiny fish is more fun than the other way around.

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I'm so happy to read this! I completely agree. I started off with seven pygmies, because that was all the store could get at the time, and I planned to buy more when they were available, to bump their numbers up to 12. Well, I didn't need to, because they surprised me by breeding in the tank, I was cleaning one day and saw two tiny baby pygmy corydoras hiding in the plant! Now they breed and the fry raise themselves in the tank, and it's even more lovely when you see a group of 20 or more swimming around together!

Since these fish live in huge numbers in the wild, you see why we see different behaviours when they're in a larger tank (yours is a lovely size for keeping large numbers of these tiny, but active and beautiful fish), and in larger numbers of conspecifics.

I'd recommend rehoming/returning the zebra danios most urgently, because of the greedy voracious eating thing, but then take your time choosing what you'd like instead. Watch videos of the fish you're interested in, and go to stores to see them in person! Pictures and videos don't always do fish justice. But they can also be pale and stressed in store tanks, so seeing both how they look in someone's established tank schooling around, and seeing them in person can help you decide. Just resist the urge to impulse buy fish when you visit!

Check out this video - this youtuber is really good and knowledgeable, a fish breeder and trader, and in this video, she'd been bought a huge school of Corydoras pygmaeus and Corydoras hastatus, and even she was amazed at how lovely it was to see such a large group of these two dwarf corydoras were feeling secure together in a huge group!

Skip to the 2::45 mark to see them!

Again, I can't thank you enough for all the advice! I am happy to hear that about emerald rasboras, and the advice about live food is something I'll look into. I would be very delighted if the cories started breeding in the tank. Unfortunately one of the six I bought was very small and stressed and died, and one more seems to be missing as well so I only have 4 swimming around; but they are lovely fish and I hope to up the numbers once the current additions are settled and I've figured out the food situation.

I wouldn't describe my otos as "gasping" but they do breathe very quickly and visibly. I just assumed it was because they are very active swimmers. Is this normal?

Edit: I will try to rehome the danios and white clouds tomorrow.

Also, repashy soilent green food just came, so I will be trying that out in a bit.

JackGulley said:

Again, I can't thank you enough for all the advice! I am happy to hear that about emerald rasboras, and the advice about live food is something I'll look into. I would be very delighted if the cories started breeding in the tank. Unfortunately one of the six I bought was very small and stressed and died, and one more seems to be missing as well so I only have 4 swimming around; but they are lovely fish and I hope to up the numbers once the current additions are settled and I've figured out the food situation.

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You're so welcome! It's what we're here for, to share our hobby, and try to help each other out! It's especially worth investing the time to try to help when the person asking for advice is as receptive as you are, and it's obvious you want the best for the fish, and we'd like to help you make sure it's a success!

It's a hobby with a steep learning curve, and a lot of misinformation out there, so can be really intimidating, confusing and overwhelming for people who are just setting up their first tank, and it's disheartening when they lose fish, or something goes wrong, and it's not their fault - but then they often end up giving up and leaving the hobby. We don't want that. We want to help people have successful, healthy tanks and fish, so they stay in the hobby!

Don't be surprised if the missing pygmy reappears at some point. Fish are good at seemingly vanishing in tanks, then randomly reappearing. If it has passed, then it's a shame, but it happens. And being newer to the hobby, it's much harder to make sure the fish in the store are healthy, so they may have been ailing before you even got them, like the otos were.

You can always add more pygmies later. I wouldn't worry about breeding them just yet, but when you're ready, I and others will be happy to share tips to spur on the fish to spawn, and tips for raising the fry, whether you collect the eggs, or just want to try to encourage them to colony breed in the tank the way mine do. (which means less work!)

JackGulley said:

I wouldn't describe my otos as "gasping" but they do breathe very quickly and visibly. I just assumed it was because they are very active swimmers. Is this normal?

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I can't tell without seeing them I'm afraid. What temperature is the water? Is there surface disturbance from the filter? Do you have a water testing kit to be able to test for ammonia, nitrites, and nitrates?

If possible, shooting a short video of the tank and the fish is the most useful way for us to be able to see them, and assess whether it's normal or not. Unfortunately, the video upload function on the forum doesn't work, but if you are able to get a video of them, you can upload it to youtube then link it here, and we can see it that way.

I'd do the repashy food first though. It sometimes takes a few tries to get the hang of mixing it.

My current thoughts for feeding plans are:
Repashy Soilent Green (For otos, snails; shrimp and plays will also enjoy)
Bug bites, ground small (For corys and shrimp, will put under something with a small opening)
Omnivore flakes (For platys and whatever schooling fish I get)

However, those live foods sound interesting too. Would those be a good food for the platys too (instead of flakes) or would they be too small for them?

JackGulley said:

My current thoughts for feeding plans are:
Repashy Soilent Green (For otos, snails; shrimp and plays will also enjoy)
Bug bites, ground small (For corys and shrimp, will put under something with a small opening)
Omnivore flakes (For platys and whatever schooling fish I get)

However, those live foods sound interesting too. Would those be a good food for the platys too (instead of flakes) or would they be too small for them?

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Oh don't worry, the platies will love them too!

Nearly all fish will go wild for live food, and it can be fun to culture food for them. But honestly, at this point, in your shoes (and mine!) I'd go for those foods, but frozen. You can buy packs of frozen fish foods of different varieties like those. Fish stores and pet shops that stock frozen fish food (worth calling ahead of time to see if they stock it, and what they have) often have larger food like whole shrimp, or chunks of tilapia for large, carnivorous fish, but you want the small food items like the ones I mentioned since you have tiny fish. But the platies, danios, WCMMs, and my adult guppies and mollies, gourami, tetra, all go wild for frozen foods like that, and even more so for live foods.

But culturing live foods is a whole new world, and can take time and energy - honestly, I only culture live foods when I'm breeding or have fry to raise, and then I culture some microworms, which are super easy to keep a culture going. Oh, and in summer, I harvest mosquito larvae from buckets or random containers of rainwater in the garden, and feed those live to my tanks. The fish go wild snapping them up, the movement from the live food stimulates them. And bonus, those larvae never turn into annoying adult mosquitos...

All of your stock will enjoy the repashy, it's a really good food, and hopefully the otos will go for it. I think it's the most likely commercial food for them to understand is food, so I'm glad you have some. But all of them will enjoy it, and the bug bites.

If they have those staple foods, and sometimes some frozen foods, they'll thrive. The frozen food arrives in cubes, and your current stock won't need a whole cube, so just shave off a few slivers of it, and put the rest back in the freezer, since a whole cube would be too much for your current stocking. I only use a whole cube for my 57g since it's a bigger tank and more heavily stocked with a variety of fish, and I give them that the day before their fast day.

You're doing well. It's nice to see someone so dedicated to looking after their fish, and I think you're going to have a beautiful and thriving tank soon, with the way you're going!

Last night I put a cracker-sized slice of repashy in after all the other fish were asleep, and in the morning it was completely gone and the otos look much rounder! I haven't been able to watch them on the glass for a picture but I'm really happy I got them to eat it. The first time I tried the gel, I did it during the day and stuck it on a rock but the platies made a big mess of it and the otos didn't get any.

JackGulley said:

Last night I put a cracker-sized slice of repashy in after all the other fish were asleep, and in the morning it was completely gone and the otos look much rounder! I haven't been able to watch them on the glass for a picture but I'm really happy I got them to eat it. The first time I tried the gel, I did it during the day and stuck it on a rock but the platies made a big mess of it and the otos didn't get any.

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This is great to hear!

Only note of caution is to remove uneaten food and maybe up the water changes for a while, while you're encouraging the otos to eat and feeding more, and while these fish are settling in, the cleaner the water, the better their chances of regaining condition. Also because it's easy to accidentally cause an ammonia spike when feeding a lot, and when the other fish like the platies are eating a lot, so producing more waste than usual.

But your tank isn't heavily stocked yet, so no need to panic, it's just what I'd do in your shoes. Keep an eye on those otos, but they've survived this long is a very good sign. If you can snap photos of them on the glass so we can see their general condition, then great, but we all know from experience how difficult it can be to get a photo of fish!

Loving the journal thread.

Here's one oto! Unfortunately the other one still looks pretty skinny (haven't been able to snap a picture but it looks the same as they did before ), I'm not sure if it found the food. I did notice that the other fish were also eating the food at night, but it might just be because I had a lamp on in my room and they were still awake when I put it in. Now that we've established that the food works, how often should I be giving it? My gut says to keep giving some every night so the other oto can learn, but I'm afraid to overfeed. I definitely saw the platys eating it but they don't seem rounder in the morning so maybe the platys stopped when the lights went out, and the otos did get most of it.

JackGulley said:

Here's one oto! Unfortunately the other one still looks pretty skinny (haven't been able to snap a picture but it looks the same as they did before ), I'm not sure if it found the food. I did notice that the other fish were also eating the food at night, but it might just be because I had a lamp on in my room and they were still awake when I put it in. Now that we've established that the food works, how often should I be giving it? My gut says to keep giving some every night so the other oto can learn, but I'm afraid to overfeed. I definitely saw the platys eating it but they don't seem rounder in the morning so maybe the platys stopped when the lights went out, and the otos did get most of it.

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That one does look much better!!

The other one may be taking longer to gain condition, and may not have accepted the commercial food yet, but the fact it's still alive (and active?) means it must be finding some food in the tank. Hopefully it's finding enough to sustain it, and it may learn from the other fish and oto to accept the soilent green.

Do you have a water testing kit?

I haven't fed repashy in a while, and don't have time to look up the details now, but I don't think there would be any harm in trying it daily, or even twice daily, so long as you only leave it in there for a few hours, and syphon out any uneaten mess that's less. I'd be trying some early in the morning after lights on, then again late at night after lights out.

But ideally, keeping a close eye for ammonia/nitrites/nitrates, cleaning any uneaten food, and making sure to only feed the other fish lightly, and water change as needed.

The other oto may also be a different sub-species, and look different from the one in the photo. Should still have a rounded tummy though. Keeping fingers crossed for you that it finds food and regains condition like this one has!

@Seisage , I'm sure you'd be happy to see this!

Yes!! That oto looks so much better
I'm so glad that you've taken the time and care to make adjustments on really short notice, and you're lucky your dad works at a pet store haha. But I'm really happy to see that your efforts seem to be paying off! Here's hoping that other oto learns and puts on some weight soon, but like Adora said, it's a good sign that it's still alive and active. I think if it doesn't learn how to eat the repashy, you might want to try the algae/biofilm farming route, where you put smooth stones in a bowl or tank and stick them in a sunny spot for a while.