I am re-reading this thread, and looking into the links more closely.
In post 85 the link (about disinfectants) specifies that glutaraldehyde is very effective (almost at the end of the article).
Glutaraldehyde is the liquid carbon source used as a substitute for Excel.
In low doses it is not toxic to fish.
If you can get gluteraldahyde, treat the tank and everything else with that, then rinse well. Any trace amount left after rinsing is so low it will not be toxic.
MAYBE the plants can tolerate the higher dose, too???