Ich treatment bad reaction

[Goshfush]

Hello! I have a 33 g planted tank, oh 6.8, ammonia, nitrate, nitrite all 0. I recently did a half dose (recommended due to scaleless fish) of blue planet white spot remedy(malachite green/formaldehyde). I did this because my glass catfish had a few spots each, none of the other fish had spots and we're all bright. After putting the dose in 3 emperor tetras died quite suddenly. All my other fish were fine except one gourami who became weak and is still very weak now 3 days later. We saved the last 2 emperor tetras (one of whom was starting to lose colour) by doing a water change and putting carbon in the filter. The remaining emperor's perked up and are fine now. All over fish including the other honey gouramis, kuhli loaches, cories , phantom tetras and glass cats are fine. Does anyone know why this medication could have caused that reaction? Any tips on how to help the struggling gourami it lies down a lot gets up and swims a little, than lies down again not really eating. Thanks so much for any thought you have on this situation 

[ange]

I don't have experience with that specific product but it has the same active ingredients as Ich-X and I've never witnessed an adverse reaction (even dosing the full amount to plecos). Have there been any other major changes to the tank recently?

[Goshfush]

Thanks so much for replying, no other changes to the aquarium it was so weird. We are now using a different medication