Are the fish is in
qt? If so, no worries you can beat it.
If they are in
qt, you can reduce the
SG pretty quickly. I would change out 1/5the of the water volume in the
qt every 12 hours with fresh
RO water. Fish can take a fast drop in
SG, but cannot take a fast raise in
SG
The hydrometer will be OK to start, but to do an accurate treatment, a good refractometer is needed.
The
PH will do some funky stuff, especially while you are adjusting the
SG down. The buffers you mentioned above will do a fine job in keeping the
PH stable during the transition. Your best bet is to buffer the change water before you use it. Also test daily for ammonia, it will spike until your biological catches up with the treatment.
Please do not attempt this treatment within the main. A proper
qt setup the most important component of the treatment.