Am I doing the right thing isolating my cory?

I moved to a 240l tank from 70l several weeks ago, it cycled within a fortnight due to running the old filter simultaneously and I used prime and water changes to mitigate the mini cycle impact . Really pleased with how it has done with everything I learnt from the first tank experience and taking advice etc, substrate is now river sand, my maintenance and water quality is really good etc. With the extra size I bought two more cories for my current cories to enjoy swimming together. In the old tank my cories were showing signs of stress from a rough black "sand" substrate but they've been really happy and looking healthy in the new tank. I've improved their nutrition too taking advice again from on here (thanks guys). Only disappointment is that I went to the LFS to get zebra loaches having read up on them but the LFS only had yoyo loaches and told me they were the same, I should have checked before bringing 6 home as I've since learnt that they can upset cories and take their food. Fortunately I haven't witnessed this and have observed them lots. They seem to all have their own space and the only issue is that sometimes the loaches are a bit lively when the cories want to chill, but mostly the loaches play at the back of the tank and the cories enjoy the front part.
Anyway, one of the new cories I noticed has no barbells. I noticed this a couple of weeks ago. He is much smaller than the others due to being new but doesn't seem to have grown like the others, and having observed him he barely gets any food. He does seem to have gone very weak as he doesn't seem to swim much or attempt to get food. So, I've put him in this isolation box in the hope he'll eat if he has his own food in there and isn't pushed around by the other fish as was seeming to happen. Is this the right thing to do or could I be causing more stress by this? He seems to be moving about more now he's in here and I don't know if that means I'm wrong to have put him in this small space or if he's moving about cos he's less stressed..
I've turned the light off cos I thought it might stress him being up near the bright light.
Just as I feel I know what I'm doing I feel like a total amateur again!!

I would not isolate the cory, he will be under less stress with others in the main tank.

Loaches and cories should not be in the same tank, true. Can you return the loaches? This would be best going forward.

I'm going to give a "gut feeling" answer, and someone may come along with something more solid.

I've seen Corys come in from the farms with their barbels burned off my ammonia. In every case, they were albinos, probably because they are among the most mass produced and cheap catfish, and there get no extra care in packing. A friend with a pet shop once sold me a bag of them because he wouldn't put damaged fish on display for his customers. He may even have refused to pay the supplier and gave them to me - it was a few tanks ago.

Some died, but most grew back smaller barbels than they should have had, and did okay. They weren't the longest lived Corys I've had, but albinos often have less resilience.

Based on that, I would keep him with the shoal. He may not survive - there are no guarantees, but in a still water container alone, I think stress will hit him hard. It's well meaning, but he is a social creature who needs moving water and companions. The wild card is the loaches - it isn't a good practice to combine two groups that both have very similar needs.

Byron said:

I would not isolate the cory, he will be under less stress with others in the main tank.

Loaches and cories should not be in the same tank, true. Can you return the loaches? This would be best going forward.

Click to expand...

I've put him back.. Thank you.
I am torn regarding the loaches, I feel sad for the fish at my LFS, they don't even have any substrate in the tanks, I feel like if I take them back I'm committing them to a doomed life.. But I don't want to stress my cories either. Other than the barbelless one they seem really healthy in the new set up especially with the new sand. I could see if there's an online group or something for local people who may want them for their tank..

GaryE said:

I'm going to give a "gut feeling" answer, and someone may come along with something more solid.

I've seen Corys come in from the farms with their barbels burned off my ammonia. In every case, they were albinos, probably because they are among the most mass produced and cheap catfish, and there get no extra care in packing. A friend with a pet shop once sold me a bag of them because he wouldn't put damaged fish on display for his customers. He may even have refused to pay the supplier and gave them to me - it was a few tanks ago.

Some died, but most grew back smaller barbels than they should have had, and did okay. They weren't the longest lived Corys I've had, but albinos often have less resilience.

Based on that, I would keep him with the shoal. He may not survive - there are no guarantees, but in a still water container alone, I think stress will hit him hard. It's well meaning, but he is a social creature who needs moving water and companions. The wild card is the loaches - it isn't a good practice to combine two groups that both have very similar needs.

Click to expand...

Thank you, that's both interesting and sad to hear.. makes sense though. He's back with his crew now so hopefully for the best and hoping he'll make it! The others have done so well since I improved their environment I'm really vested in him doing ok!
I've learnt more on this forum already than any amount of googling and certainly more than the LFS have helped me.. They don't even have substrate in the tanks and some of the fish are there for months and months.