Firstly I think you would get much more help if you could post in the 'African/Old World cichlids' section, I know it`s a bit confusing when you`re new here so maybe one of the mods could move this thread for you
Secondly, I have a Tanganyika setup that has some heavy pieces of ocean rock in it and I did put some plastic drain grids in the bottom of the tank to rest the rocks on. There`s also something called egg crate (plastic grid sheets) that can be used as well, polystyrene isn`t much good as it crumbles into small bits and will float.
I have a powerhead in my tank and it helps a lot to push waste towards the inlet of my filter.
Have a look here for some info on the kinds of setups there are:
http/www.fishforums.net/index.php?/forum/13-african-old-world-cichlids/
I had an airstone in my Malawi tank.
Despite what you read, cichlids don't really like a strong water flow. They can be found at depths of 10m plus in nature where there is little wave action.