Sounds like an awesome shed Kahuna, got any pictures? I'd like to have a few kinds of cories as well. I'll probably start by trying to breed the skunk cories I have, then maybe get some rarer ones.
What do you mean by a "closed loop system"? I was planning on running 3/4"pvc all around the top of the room and branching off of that for individual racks with more pvc, then finally tap into the pvc with valves connected to airline going into the tanks.
I'd like more details on your plumbing system as well, I've spent hours pondering how to do everything and change my mind almost daily. I guess ideally I'd have air, aged water, and a drain going to every single tank I think. That's a lot of plumbing though...
1st forget all that pipe for air 1/2-3/4" flexable tubing and hose clamps. Less glue measuring and work all the way around. Build manifolds for distributing the air 8-10 tanks and install the valves in them. The cost is a little more but the installation is 1/3 rd the time and you can move it around if you decided to expand or rework the inside with no more glueing cutting etc.
I am installing drains every 3 tanks around the shed. My racks are 3 tanks high 9 per drain. I installed 2" PVC and ran the drain under the bottom rack with the uprights for the drains running against the upright studs for the racks. Now I can put a fishing weight on a 1/4 3/8 hose and stick it in the tank and walk away. When it reaches the desired height it stops draining. I refill by gravity my aged water is upstairs just garden hose here with a little valve to turn on and off.
By closed loop system on the air I mean no dead ends everything is hooked to everything like a giant circle with spokes all hoses meet each other somewhere none dead end by them selves. Think of it like Karma Man. You will also find the flexible tubing easier to moch up to see how you like it.
There is a pic thread of some of my shed already here when I am done reworking it I will post the new ones. Just took down 1 rack and reworked it for more small tanks.
I used 2xs for my racks of 10s I purchased a rack from loews 187 bucks industrial steel 2 ton per shelf 3 shelves that holds 18 15s or 20 longs 6 per shelf sideways not long ways. All my tanks right now you look in the side or end not front or back. Thats how I crammed so many in the shed.
Msjinkzed hubby is a welder very fine shelves there from the pics.