How long to quarantine a pleco for ?

[Minifish]

Hi,

Looking for some advice, 

I have a small pleco who is currently in quarantine after his 3 tanks mates died 10 day after being brought . The 3 were large and hogged the food I am unsure why but they were fine one morning and by the evening they were floating up right . I did by a new bog wood and some new food so it could have been either . 
 

I removed the one survived into an empty fry tank . But left the plants and snails in the tank where the fish died . They seem fine but I don’t want to put the pleco in incase it was an illness that killed the plecos. I was hoping to put him a tank with my breeding fish he should be fine with them . 
 

How long after his tank mates dying should I wait he seems healthy and eating. My issue is the fry are out growing the fry boxes they are in and will need to moved in the next week . I don’t really want to have to set another tank up at the moment but don’t want to risk if it’s an illness the rest died from . 
 

many thanks 

[Guppysnail]

I’m sorry for your loss. Usually 4 weeks past the last sign of illness or death. This gives the illness time to present in the fish as well as any other issues to show up.