This might be a little pricey, but we just used a Starwall system to build out our office space. It offers the same type of panels you are looking for, framing can be customized any way you like, they offer painted mdf or laminate solid panels, framing is with aluminium components. You'd be looking at the cost of framing, panels and installation. The nice thing about this system is its fast to install and can be modified at any time and easy to remove.

The last thing you really want to do is tie a furnace cold air return into a fish room, evaporated salt water will eat up ducting and furnace components quite quickly. You need a separate exhaust fan. Unless you're going to seal everything with lids (sump and tank) you're building a classic mold closet, I've seen at least a dozen of times in my days.

I'd stick with the melamine, it's cheap enough to replace down the road if need be and if you do a good job on the edge band it will be pretty well sealed.

Regardless of what material you use, it won't just float there. You'll need to build a 2x4 skeleton that will hold all the panels in place

Here's an idea of what I'm referring to. I love the look you are trying to achieve, very classy and elegant and makes the tank just pop!

http://www.starwall.com/starwall_ftp/Gallery/

Marko, totally agree it needs a skeleton. This system offers exactly that...no I'm not associated or affiliated with this group, but I've seen their work on many projects and its amazing what can be done with this system, don't have to have straight lines in the framing, angles, odd shapes etc.

This just show how well i plan this hahaha, ok so now i need a exhaust fan, darn, not sure how i am going to hook this up to the exhaust duct in the bathroom next to this fish tank.

Make me just want to scrap the whole project all together :-(

If you want it done right you'll need a separate vent, as just tying into another vent might not work too well seeing that you might just end up venting the humid air from the tank into the bathroom. If the tank is on an outside wall which I seem to think is the case then drill a hole right through the wall, easy!

Otherwise keep the tank open, as in not in-wall.

I agree with the idea of a separate exhaust fan to the outdoors, and hooked up to a humidistat
Then you adjust the humidity level you like

Drill through wall is not an option because wife would kill me :-), and if we decide to move, gonna have to patch it. So is it fine to seal the cold air return and have the fan to vent the air to other room?

yes....this would be the cheapest and easiest thing to do.....get the moist air out of the "closet" and into the main area and let the HRV take care of the rest.......

Agreed