You've only got about 40x turnover in your 155 by the sounds of it... which really isn't so strong that nothing can like it. It could be more your coral
placement, rather than flow.
2500GPH in your 165 is only going to be 15x turnover + return... which isn't enough for SPS for sure.
I would run 4 holes down the middle of the bottom of the tank, and the intake mid-way up the back wall, or at least high enough that its not sucking sand up.. You may want some ball valves before each return bulkhead so you can adjust the flow in each 1/4 of the tank.
Couple pics of how I plumbed mine.
Like I said, run the intake on the back wall, not the floor like me..
