I find that 7 inches is the best. This is because I have 6 inch lids. This also gives you plenty of room to get your hand back there and mess with equipment if needed and leaves room for almost all lighting options. The 7 inches also gives you plenty of room for netting fish.
I have done smaller racks with less space between rows and it was very difficult to net fish, mess with equipment, etc...
All of my tanks go in long ways to fit in more tanks, with custom lids. I highly recommend custom lids as they are cheap to get cut and that six inch opening is awesome. Just make sure you have them sand the edges of the glass or its going to look like shark week in your fish room...
I have done smaller racks with less space between rows and it was very difficult to net fish, mess with equipment, etc...
All of my tanks go in long ways to fit in more tanks, with custom lids. I highly recommend custom lids as they are cheap to get cut and that six inch opening is awesome. Just make sure you have them sand the edges of the glass or its going to look like shark week in your fish room...
