Extend a 75/90 G stand to 120G stand (48 x 24)

Hmm. I've done 3 inches, so I guess 6 would be ok since it's not in my house. If you think the stand can hold the extra weight, you can expand the top with some good quality plywood. I'd be nervous about it, though, and it would look goofy. How about we make you a new stand instead?

It all depends on your current stand. You could build a 6 inch wide part but you will have to be really good to make the perfectly level. I would build another stand. I dont think that it is worth the chance of having 120 Gals on the floor.

MAHA

I don't think it will hold very well, especially if your stand is fake wood.

Hey maha!

So I'd need to see a pic of your current stand, but it's doable. If you're handy enough with tools then you should be able to build a 6" platform the same height as your current stand. Attach the 2 closest legs of the platform to the old stand. Then lay a 2'x4' sheet of ~1/4" ply (1/2" would be better, but you do what you can with what you have). Screw it in, making sure you sink the screw heads below the level of the ply. Put your sheet of styrofoam and you're good to go.

btw, put some sort of brace between the legs of the platform or skin it w/ ply or something to make sure they don't bend the screws.