OTher than possibly contaminating your freshwater with the little bit of residue from the saltwater, you can basically use the same equipment between both. Just make sure to do a good rinse in between the two setups. OBviously the test kits have to go with the respective tanks, although, I found out that the ammonia test is the same for both SW and FW...the colors are just a little bit off. As well, a high range pH test in the FW kit can be used for SW since that is all the SW pH is..higher range.
I use to run both fresh and salt as well and I was pretty paranoid. I had a blue bucket and net for the saltwater and green of each for the freshwater (blue is more of a marine type color in my mind
) The two never touched the opposite tanks. I also routinely ran two seaprate siphon hoses but as long as the hose is rinsed very well in between, it shouldn't be an issue. SW parasites can't really exist in FW and vice versa.
BTW Russ...I love the cave
It always seems that the hardest part of setting up a reef is getting the LR JUST right.