lucky lucky.
I use Seachem Flourish to bump phosphate from time to time without issue, but not with Excel. Flourish acts like a fertilizer and excel acts the same but through C02 adds. So you’re right, a double shot. One or the other if you need to bump for plant stuff. They should do well in a .1ppm to .3ppm range without overtaxing your filtration, or making corals unhappy.
So glad you were able to dodge that one!