Question: How long to ISO?

I just bought two male juvenile CFB about two days ago (may 19th). They were both very thin at the store, one was very active and was swimming and walking around the tank the other was completly out of the water. Which I know isn't a good sign. Their tank set up was not a set up for these guys. It was a 20L tank with gravel and one little rock, one fake plant that they could barely hide in and a huge rock turtle filter making current in the water. And when I asked what they were feeding them they told me it was fish flakes, well no wonder why they were so thin!
Anyway, I brought them home and both are eating, iv decided to feed them everyday to help get there weight back up. Also question I bought omega one frozen daphnia and then another package of chopped frozen shrimp. Are these good foods to feed along with frozen bloodworms, brine shrimp and live blackworms?
So how long do I ISO them before adding them to the main tank? With my adult male that iv had for over a year?

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If you see signs of illness, I would isolate for at least 3 months, if not 6 months, past when they appear healthy and normal.

It's doubtful they'll eat frozen daphnia or shrimp. Live, tiny food is the best. Blackworms, earthworms, bloodworms, waxworms, etc.

Thank you. They do not seem to be sick besides being thin. So far they are eating the bloodworms and live blackworms but will not touch the brine shrimp. I'm going to try tubifex worms. I was able to get frozen not live. Ill keep them isolated for a while, and see how it goes I guess

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Well its been over a week with these guys. One is gsining weight and I can clearly see it. Snd he is fully aquatic, he just wants to swim and eat.

Now the other still clings to plants and sticks himself on the walls of the tank completly out of the water. I haven't seen him eat since the first night I had him. Still pretty skinny. As you can see in these picts. Any ideas on getting him to eat? Why would one be active and have full appetite but not the other?
First two picts is Chicken the fat minded one. Last picts are Noodles

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