whats wrong with using metricide 28?
As far as I know you can use either. Metricide 14 is a little more concentrated at 2.6%. Metricide 28 is 2.5%. The MSDS for Metrcide 28 lists sodium nitrate. However, I think this is in the small activator bottle which you don't use anyway. Metricide 14 is generally cheaper as well.
Metricide 28 MSDS
Metricide 14 MSDS
Will this stuff work the same as excel in terms of controlling algae?
Yes. They are the same thing with the exception of concentration. Excel is 2% glut.