We probe counter-ion specific effects in nano-confined electrical-double-layers (EDLs) by means of direct force measurements across a model slit pore in the extended surface forces apparatus. By variation of solution composition, we compare four different counter-ions with dissimilar hydration properties, namely Na+, K+, Cs+ as well as H3O+, all confined between (0 0 1) mica surfaces. We discuss the results in terms of a recently proposed pi-transition model, evoking hydrated ion layering as the recurrent structural element in highly confined EDLs. We demonstrate that the pi-transition essentially proceeds in multiple steps in coherence with the event of single- or multiple- hydrated-ion layering. (C) 2017 Elsevier Inc. All rights reserved.