I'd have to side with cricketman here.
When you are eating fish and chips, the fish is dead and was humanely killed. It's mot like I'm pulling out a fish out of the water and eating it?!
IMO you are not minimizing the fishes pain because how do you know that it hurt more having this thing on its eye, than having you cut its eye open and pour furan 2 in it? Just imagine yourself in its shoes, you get pulled out of the tank (stressing you) then having your eye (tumor) being cut open and this stuff poured in there. Then your back in the tank and its bleeding like mad. This could have made the fish even more stressed, opening it up to more diseases. And what did you cut the eye open with? Was it properly sanitized? Did you wear gloves?
And to agree with Sophia, that he may have been better off dead. The fish would have died quickly, with little pain. And if you do save it, it has to live the rest of its life with this condition that may or may not get better. This decision at the start would have saved you the money.
Did you even talk to a qualified person? I'd love to hear their opinion on this (about the cutting of the eye)
Also, how do you know it's a bacterial infection? And if you used two full packet doses, then are you sure it's going to get better? I know it may look better, but how do you know that on the inside it's getting better? For all you know it could be really bad, and that this tumor is one of the final stages of the infection?
Yknow all these things matter, and as a teen my opinion may not be as important as say yours or a qualified person.