Wood under tank
 

I have a 110gal 48x24 footprint going on a metal stand. What type of wood should I used underneath it. And how thick.

I would use 3/4" plywood then an inch or so of styro if your tank has a flush bottom.

Should I paint the ply with anything

I would paint it with a couple coats of paint. I am sure someone knows of good water resistant paint.

just paint a few coats of good exterior paint

I have a metal stand too, I am in the process of building a wooden structure around it to close things in and make it look nice. At the hardware store I asked for wood that wouldn't deform to much if it got wet and the staff told me to buy birch plywood and for paint they sold me interior/exterior plastic enamel which is supposed to seal really good.

Anyway HTH

I have a metal stand, and I'm using a sheet of 3/4" plywood with a sheet of 3/4" foam on top.

If you are really worried about the wood getting wet, you can use marine grade plywood.

I have plain old run of the mill plywood under the tank, and I've never really gotten it wet. If it's ever been wet, it's just a slight trickle.

As I assembled my tank this is one of the things that continually crops up... there is always a better way to do something and you can honestly drive yourself nuts trying to get them all. For instance, I primed the plywood that will sit on my steel stand and then painted it with 2 coats of an oil based water resistant paint. But perhaps a eurothane type sealer would have been better. I used Tremclad on my stand to make it less likely to rust, but apparently Rhino liner is way better. I've got the white styrofoam on top of the plywood, the type I've used on all of my tanks over the years without issue, but then I read that the pink stuff is better. I used 3/4" styro and now I see that many use 1". My stand is 1.5" steel but many recommend 2". I plan to hang my lights from the trus joists above the tank and I'm warned that the ductwork cuts through the joists and they might be weak so I had to put some gussets in. It's enough to send you over the brink. No matter what you do there is always another, better way to do it. So do your best and live with your decisions. I would paint the wood with waterproof/resistant paint, though I've never done that before on any of my tanks.