Using it as a last resort I think is exactly why it might be harmful. Your tank is already on its last legs and probably nutrient soaked to the pores, what happens when you suddenly massively kill all the nutrient trapping organisms in a closed environment? A room full of dead bodies.
I think this stuff works best as a maintenance item at the first sign of trouble not after you already have a huge problem.
I think this stuff works best as a maintenance item at the first sign of trouble not after you already have a huge problem.