Yeah, slowly increase the temp to 82, and treat the whole tank. Be careful of what meds you use as some can harm plants.
As for the water stats thing. Here is the basic version. Fish produce ammonia, which is highly toxic. In the filter a set of bacteria develops to turn the ammonia to nitrIte. NitrIte is also toxic, and another set of bacteria turn nitrIte into nitrAte. NitrAte is non-toxic for fish, and as your dad said, nitrAte is used by plants. Ask your dad if he has a test kit for ammonia and nitrIte, those levels should be at zero or there is a problem in the tank, and they are major causes of stress.