He's a cutie! I agree with Sweeda, a pH of 7.8 is fine. Mine is at 8.2 and I don't have any problems.
The reason why reducing pH in aquariums is not encouraged is because it has to be consistent. If you change your water, you better hope that you either have a high KH to counter the effects of just dumping water in, or you have to properly measure out the correct amount of adjuster to keep the pH stable.
I think you should just acclimate him slowly if you feel that the pH change would be too much of a change (what is the pH in his cup?)