Circulation in the tank is pretty good; I have an FX5, 2 - Eheim 2217's, 2 - AC110's, a Koralia 3, and a old Maxijet powerhead. I might be adding another Koralia 3 once some fish get moved around.
I've had 3 Tigs in a tank at one point that ranged from 15-18" and they were fine. Main thing is foot print of the tank. Give them enough space to have their own spot, since they are territorial and they seem to be fine. I believe Nishant (Katfishguy) also had several in his tank.
Looks good. Tigs are my favorite catfish.
Here was a picture of the two of the three in the tank.
R.I.P. false tigrinus. Seeing these makes me want another one so bad! Mine just passed with no visible signs or symptoms. Those all are very nice specimens.