Pygmy cory having some problems

One of my 8 pygmy cories has been lethargic and having troubles staying upright.... here's the full emergency template

Tank

What is the water volume of the tank? 10 gallons
How long has the tank been running? Began cycle beginning of April, fish went in May 1
Does it have a filter? Yes
Does it have a heater? Yes
What is the water temperature? 78-80
What is the entire stocking of this tank? (Please list all fish and inverts.) 1 Male betta, 8 pygmy cories

Maintenance
How often do you change the water? once a week
How much of the water do you change? 50%
What do you use to treat your water? Sachem prime
Do you vacuum the substrate or just the water? Both

*Parameters - Very Important
Did you cycle your tank before adding fish? Yes
What do you use to test the water? Api master liquid
What are your parameters? We need to know the exact numbers, not just “fine” or “safe”.

Ammonia: 0
Nitrite: 0
Nitrate: 10-20
pH: 7.8-8.0

Feeding
How often do you feed your fish? 6× a week
How much do you feed your fish? 2 omega one catfish pellets for the cories, and 4 pellets for the betta
What brand of food do you feed your fish? Omega one, bug bites
Do you feed frozen or freeze-dried foods? Yes, frozen bloodworms once a week

Illness & Symptoms
How long have you had this fish? Since may 1- 2.5 weeks
How long ago did you first notice these symptoms? 2 or 3 days ago
In a few words, can you explain the symptoms? One cory is alall by himself, not moving unless startled, lying on his side sometimes.
Have you started any treatment for the illness? Not really. I just put him in a breeder box in the main tank with some Indian almond leaves
Was your fish physically ill or injured upon purchase? No
How has its behavior and appearance changed, if at all?
Appearance no, behavior yes, he is staying very still and not always upright.
Explain your emergency situation in detail. (Please give a clear explanation of what is going on, include details from the beginning of the illness leading up to now)
So 2 or 3 days ago, I noticed one of my cory cats was not schooling with the others, but was lying right next to the glass with clamped fins. He moved when the betta swam by him but went back to lying against the glass. I tried to catch him to put him in a breeder box to keep an eye on him, but he was feisty enough to not want to be netted and I didn't want to add stress. Today, the other 7 cories (and my weird betta) were all snacking on catfish pellets, when I saw him lying on his side in the grass. I actually just thought he was dead, but he wiggled just a bit when I netted him. It was very easy, though. I now have him in a breeder box to keep an eye on him and keep track of him. He seems to slowly tip over onto his side and then startle back upright again. He doesnt leave the floor. He doesnt seem to have anything physically wrong with him. His fin is no longer clamped. First photo is from the first day I saw him with the clamped fin, second two are from today.

 

Yours doesn't look like that it is in a bad condition. I had an albino corydoras that had the same symptoms as you and was swimming vertically to try to get air... and would sleep on floating plants. No one knew what was wrong with her, but she was pale in color, so I just assumed it was some kind of bacterial infection or nitrate problems. Nothing else in my tank was affected.. could have been from stress.
Now that I think about it, I doubt that it is because of nitrate poisoning, but corydoras are pretty sensitive to parameter changes. I would take the pygmy corydoras out of the breeder net/box and let them stay in the tank... unless their symptoms get worse. Sometimes there is just no defined "problem" that your fish has. I would still does Prime, StressCoat, do water changes more often, etc. I can't seem to find anything wrong with your tank, so that's the best I can offer. Best of luck to your corydoras (corydoras is both singular and plural, it sounds weird, but that's the "proper way" LOL)

 

Nothing you posted stood out to me at all. Perhaps he just came in weakened genetically.

It's great that you had a breeder box-is there anyway to shade it a bit or put in some floating plants so it feels a bit more secure.

I don't feel there's anything more to be done-what about you?

 

Nothing you posted stood out to me at all. Perhaps he just came in weakened genetically.

It's great that you had a breeder box-is there anyway to shade it a bit or put in some floating plants so it feels a bit more secure.

I don't feel there's anything more to be done-what about you?

I put in a bunch of pieces of almond leaves after I took the photos for shade and cover. I'm really not sure what else I can do, aside from keep an eye on him.. it just doesn't seem to hit any points for any specific illness

 

sadly this little one passed away today i'm still confused as to what went wrong with him. my other 7 are happy and healthy (although spooked, because i had to move some rocks around to get out the little body and that was TERRIFYING). I didn't think to take a photo of the body, but he looked really thin- i wonder, with his lethargy if he was just being out-competed for food or something. other than that, his body looked fine... no spots, growths, rotted fins or eroded barbels. hopefully the rest of them stay strong and happy!