i might use concrete board around my setup. for inside the wall around the tank stand, i'm going to paint it all, and seal all the joints/cracks with caulk.

I have regular drywall on 3 sides of my open top 38G tank. No problems so far after 4-5 years.

Although my the stand on my first tank was MDF (plastic coated) and had no signs of damage in 3 years, was always a concern. Have had other furniture made fr the stuff and doesn't to take much water to get it to swell. Guess if sealed really good, dab of silicone in the screw holes before fastening, etc..

There is MDF sheet with good moisture resistance qualities. Also, there is one type that is also formaldehyde free. Once I remember the name of the product I'll note it.

the frame holding the tank up is going to be steel and the cabnet fram will be 2x2 wood, the MDF will only act as a skin for the cabnet like you would use oak plywood or drywall, ect.. I was originaly going to do it out of oak but decided it wouldn't suit the room and decided I would rather be able to paint it.

Steve

Realize the MDF was wall covering only, just relating my concerns about MDF.

My tank isn't in-wall, but when I framed up then drywalled the mechancical room for my basement sump used the green aqua board throughout.