A couple of notes about the spider valve. First, it requires a good deal of pump pressure to work. I had to use a more powerful pump to get it to function properly, or at least to get it to switch properly. Second, while it does divert the flow, I'm finding that there is flow coming out of at least parallel channels if not all channels. This may be due to the fact that the spider valve is located below my grow beds, so there's a little bit of head to climb before the water comes out, but I'm not sure.
In my system, where I want the flow to move slowly through the sand, it's probably not an ideal way of doing things. In hindsight, it probably would be best to have a slow pump going to both grow beds and an aerator running constantly versus using a spider valve to switch between the growbeds and using the two un-used feeds (there are 4 channels on the spider valve, and I have 2 grow beds) to cycle the water around in the tank for aeration.
We'll see. I'm also curious to see if the sand system is more efficient at removing the nutrients. It had better be, because I'm probably only running the entire volume of the fish tank through twice a day - again, due to the slow inflow.