New Espei not joining existing school

[Canuck AquaTropix]

I have a 30 gallon planted tank with several fish including 4 Espei Rasbora that are doing well. Three weeks ago I picked up another three of them (a bit smaller) to make the school larger. Since I got the three new ones all they do is hang out in the top corner, it's been three weeks now. Why are they scared to join the existing school?

[nabokovfan87]

Can you share your water testing results including temp?  A photo of the setup does help as well to see what's going on a bit more in detail.  It could be something where it's a water quality issue, oxygenation issue, or something else.

Acclimation does take time and hopefully the fish are ok.

[JChristophersAdventures]

@Canuck AquaTropix It may simply be an natural part of the socialization process, however, I would observe them vary closely for signs or behaviors indicating illness, too. Since many diseases can take 3-4 weeks or more to show up, that could also be a possibility. If everyone else is doing okay, then hopefully your water parameters are doing okay, but keep testing those as well.

A lot depends on the quarantining process of the source of the fish, your acclimation process and how much difference there is from their water parameters to yours... the bigger the difference and the faster those fish were pushed through the retail system, the higher the stress and the longer acclimation will take... also the more likely you may need to treat with meds.

Are the new fish in the corner eating okay? Also make sure they are getting some food right where they are, since they are not actively seeking it out on their own right now. I know it is an additional trouble and expense, but it is a good idea to have some basic meds on-hand if they are ever needed.

Hope that helps.