Lid for tank

I disagree,  unless the stain/finish gets IN the tank it is of no real threat to your fish.

You should however make 100% certain that the top is cured so that no vapors are being released anymore.  you know the whole apply in well ventilated area thing.

as far as the stain you use, i would just find a minwax water based stain that matches what you have.  stain it until you are happy with the color or possibly just a touch lighter than what you want the final product to be.

i would then do a minimum of 3 coat of a water based polyurathane in "gloss, semi, matte" according to the shine you want the finish to have.  the poly is going to be the best protection you can easily achieve against mosture.  these 3 coats will darken the stain below just slightly, and more "yellow" it than darken it in most cases.

if you get really worried you can look into something called "spar varnish" which is what boat builders finish boats and things with.  unfortunately it has a VERY long drying time which will turn your project from a week of finish applying into a minimum of a month.

as far as the store did they happen to mention waht this "special stain" they know about actually is? i'd be curious to hear what they think is going to kill the fish that isn't in the special version.

The person I talked to at the store said he had a fresh water tank and stained the top and in a short time his fish went belly up. He watched the water get on the underneath side of his lid then drip back into his tank. This is what he thought killed his fish.

Another option is an epoxy paint finish.  They are impervious to anything and don't have the curing time of a spar finish.  The key here is making sure you cover the entire surface.  Any little pinhole exposure will enlarge if moisture gets in it.

Don't sweat it!  Buy whatever stain/top coat you like and just do it.  Let it dry before using and you'll be just fine.

I think epoxy paint is overkill for what you need, although a good idea.  Aluminum reflectors will reflect FAR more  light than white paint as well.  I still think you should stain as you see fit and then do 3 - 5 serious coats of polyurathane and never think about it again.  i have built several stands and my current one has had the lid on it for 2 years now with no problems at all (and that was only 2 coats of varathane)

http://www.utahreefs.com/forum/forum_posts.asp?TID=8215