Hey, I've had good luck with Ick Guard and it didn't discolor anything in my one of my ten gallons. However, this might be a different kind of Ick Guard then you may have, mine is a slightly dark blue color, made by Jungle Corp.
My girlfriend used a product, called Quick Cure, worked for her but it did stain the silicone on her tank. Don't know if it's same one as mentioned but thats what I know about it.
They also have a Ick Guard II (well around here they do) that's made for catfish, loaches and all types of bottom-feeders, anything pretty much scale-less, and it works great, doesn't stain anything either.
I've have good results with the both I've tried, so I dunno.