tuning causes floppiness.

for my new band i use the tuning C# G# C# F# on a jazz bass, the top string is kind of floppy, i use ernie ball super slinky's, this might belong in the string section but i wasnt sure, but what can i do to tighten up the string a bit more, should i try different gauge strings, different company, of what kind of set-up specs should i think about.