Copper is usually only an issue in some of the water soluble salt forms, such as are used for treating ich or in snail control products.
The amounts in most fertilizers and foods rarely, if ever, causes problems in inverts. Even copper pipes don't cause a problem.
Flourish ferts and Excel are quite safe used as directed for inverts. I've been using them for over a year on a shrimp only tank full of plants too, not a single problem with either one. Just don't overdose, or 'guessitmate' a dose. Measure it properly. Too much Excel can harm some plants that are sensitive to it, such as Vals.