What to watch for in observation-only quarantining?

[redmare]

I got 8 panda cories and a baby longfin BN pleco in the mail on Tuesday, and set them up in a 12ish gallon plastic tote with heater and extra sponge filter from my main tank, along with a big piece of driftwood for shelter and tannins. I tossed some clippings of bacopa in there too. Being in Canada, I don't have access to meds, and since they're catfish, I don't wanna go using salt if I don't have to. My plan is to just keep an eye on them in the tub for 2 weeks before adding them to my 30 gallon with 4 male guppies and 5 honey gouramis. 

I was wondering if anyone had advice for observation only quarantining. I know to look for things like ich, fungus, fin rot, stuff like that, but I was wondering if there were any other things I should really keep my eyes open for. They all seem to be doing really well so far! They're eating great, they weren't super underweight when they came in and they've gotten happily pudgy in just a few days. They're pretty tiny though! They're very bold, love to rummage around and play with each other, like to play hide and seek in the driftwood... basically the cutest little things. The little pleco is doing well too! She's pretty bold, she loves munching on her wood and likes to see if there's leftovers from the cories. I've been feeding repashy community and soilant green and bloodworms. 

I am also having a small nitrite reading- 0.25 or so. Doing daily water changes to keep it in check. Any and all advice on quarantine or the panda cories/bn pleco is certainly welcome!

[Colu]

Rapid breathing at surface odd swin behaviour  not eating loss of colour

[Colu]

I feed my pleco hikari algae wafers Sera wood chips and 3times a week cucumber and spinach peas

[FrozenFins]

stressed fish, fish stop eating, sunken bellies, and any symptoms that don't seem right. It tooks my pleco a solid month before he sarted coming out of his cave, now when I do see him, he scurrys away really fast.

[Hobbit]

I have some plecos in quarantine so I’m following this thread. How do you know if they’re eating? I’ve offered three kinds of food so far and I’ve never seen them eat any of it, but I’m not watching them 24/7.