Sorry I am a bit late to the party...it has been a busy day. The biowheels in the Emperor are a great "wet/dry" filter. They provide a great place to process NO2 into NO3. In a way, that is problem with them in SW tanks. The bacteria needed to convert NO2 to NO3 resides in an aerobic (with oxygen) environment. The bacteria that consumes NO3 resides mostly in an Anaerobic (without oxygen) environment. This is why submerged LR and your substrate do such a good job at controlling NO3...provided you have enough to process the waste produced by the tank. That said, if you have plenty of other biological filtration in the tank you will likely not notice the NO3 that can be produced by the biowheels. On the other hand...why bother with them is they serve no benefit? For a SW reef application I say just remove them. Of course, there are many other factors that weigh into the NO issue...such as feeding, stocking, over-stocking and water change schedule.