Excel - How long is it good for?

I have a bottle of excel that's been sitting on the shelf under my tank for well over a year (probably closer to 2 years at this point).

Just want to be sure that excel doesn't go bad after a certain date. There's no mention on this on the packaging so I assume it's probably ok.

I have a problem with some hair algae in my tank and I've read on here that daily doses of excel should help so I figured I would give it a try.

Thanks everyone!

After doing some of my own research online, the closest thing I found to a definite answer is here:

http://www.aquaticplantcentral.com/forumapc/seachem/34701-product-shelf-life.html

Thought maybe this would help other people out.