Wow, i didn't know 6100 that powerful. I install 4x6100 into a 4x2x2 with DSB and he doesn't have any problem with sand storm. Let me guess you put the pump on the back wall facing the center front panel. It may work good but most of people will have problem with sand get blowed around. Let try this guy and you tell me if it work out for ya.
Put your tunze on the side panel facing each other, set your controller on interval 2 then go head and turn that bad boy to 100%. Make sure pump 1 on channel 1a set it at 100% 1b at 30% the same with pump two. trust me guy. if you ever have sand being blow around i will quit posting in this forum. The problem you all running into is pointing the pump into the center front panel, too much flow will create turbulence therefore your sand got stirred up. Give it a shot and let me know. I have two wavebox and two tunze 6200 in my 48x48x24 cube and i don't have any problem with sand storm. By the way, i know what i am talking about cuz i install customer tank every weekend.