Just a little warning guys, Metricide is a toxic chemical. Take care when handling them. Don't breath it, touch it and obviously, don't swallow any.
And chemically it's not exactly the same as excel. Excel is derived from Glutaraldehyde which makes it a bit less toxic to plants and animals.
There is no proof that Excel is somehow safer than Metricide. Please read the MSDS for each product. What leads anyone to believe that it is safer when the MSDS indicates that both are of the same risk is mind boggling to me.
Further, this "glutaraldehyde" derivative is an unknown compound. Seachem said years ago that they would elaborate after getting it patented, but was unable to secure a patent. This leads me to believe that it is nothing more than a diluted version of Glutaraldehyde, just like Metricide.
Metricide is NOT pure Glutaraldehyde. It is diluted and continuing to perpetuate that it is somehow some nasty chemical and Excel is like bottled water is both irresponsible and false.