Sorry to here it mate. It really is a delicious looking scape. T. Barr speculates that in certain species Excel interferes with certain proteins that facilitate nutrient uptake through the leaves. Bladderworts, liverworts, Vallis, Egeria densa and a few others seem to be susceptible to varying degrees. Some are OK when dosed per bottle but fail when subjected to overdose. Most plants, like HC absolutely love the stuff and respond immediately. You might be able to save what's left if you do massive water changes and dose + CO2...
Cheers,