The trim around the tank is just a thin veneer that is already stained. It probably has a coat of polyurethane on it as well. If this is the case, then you won't be able to stain it easily.
Try a small section on the backside of the tank first. If it works, great. If not, try sanding another small section on the back of the tank. Try to remove as much of the polyurethane and stain as possible, without sanding right through the veneer. After sanding, try staining it the way you like it. Again, if it doesn't work, it's hidden in the back.
FYI, paint won't take on top of polyurethane either. You'd have to sand that down as well. Try it on the back also......if the staining doesn't work.
swimmer