Here's my two cents as well. I agree...you don't need the wet/dry. Filtration in a reef tank has a different definition than what we're used to in FW
tanks. The LR
is the filter. The skimmer takes out a lot of the gunk that would otherwise break down into nitrates. One reason for have good flow through the sump is to make sure the skimmer gets plenty of water to skim. Basically, and this is kinda oversimplified I guess, the stuff the skimmer pulls out is what you're used to seeing on your diryt filter cartridges in a FW
tank. I would go with the largest sump that you can fit in the space you have...within reason of course. I would also plan to have partitions in the sump for several reasons. One: You want to maintain a constant water level for the skimmer to operate in. Although some of the larger skimmers are not affected by the water level as much, most of them need a fairly constant water level to maintain their adjustment. Two: Bubble control...you're going to have a lot of water flowing through the sump. Cascading water = bubbles and you don't want those bubbles pumped back up into the main tank. Partitions in the sump that force the water to flow over and under them will cut down on the bubbles a lot. Three: If you have room in the sump, at some point, you can have a refugium in there. The sump isn't the ideal place for a fuge, but it will certainly work. Four: Partitioned chambers make great places for GAC
and/or other adsorptive media.
The larger sump will also give your system a little more stability due to the increased water volume. This doesn't mean you can add more fish though...keep the bioload right for the 90 gal
tank capacity. It's also a pain to have all your equipment crammed together. Using a big container for a sump will allow you to spread things out a little which will make maintenance easier. Last, for a return pump, I would suggest one of the external models. They are usually stronger and have air cooled motors so they don't add as much heat to your water. I like the Blueline pumps although Little Giant and Iwaki also make very good pumps. Most of them are rated at 3-4' of head too.