Are RCS bothered by the current of the Fluval Spec flow on the lowest setting? Mine almost seem like they're surfing through the water, but I can't tell whether they're getting enjoying it or hating it.
If you feel like the flow is too much (I thought it was too much for my betta), an easy fix is to make one or two small (about 1-inch) slits in the rubber pump hose. I saw someone else mention this and it works like a charm.
I have blue pearl shrimp in my fluval spec... it seemed like high flowrate however i cut a sponge and inserted it inside of the uptake tube itself... so water has to push through it to come out of the filter... i did this because i didnt want to cut the tube in case i change things in the future.
I switched from the seran wrap to just disconnecting the nozzle altogether, and letting the lift tube vent inside the pump cavity. The excess flows through the hole in the divider slowly. This way, there is no back pressure in the pump. Seems to work great. I can see some water movement due to plants waving in the stream coming out, but it is slow enough for the betta and Amano shrimp now to mind.