OT - help with tropicals!

Hi!

I am babysitting a tank of tropical fish while they are away. 70(?) gallon
tank, mix of fish, fairly new (6 weeks)..... I go over daily to feed and
remove dead fish.

I was warned one looked sick when they left, a gourami which did die and two
guppies died.... Now one of the sharks is looking bruised and battered and
has a large whitish spot on one side and it has tremors.....

Do I go back and remove it before it dies or just wait it out.
Should I expect this level of die off?

I am feeding according to instructions and she did the chemistry the night
before they left. I have to assume there were no problems and that a water
change was done too....

They are gone for another week and are in Europe, so reaching them will be
difficult....
Thanks for your help!
Cheryl