Live food can carry parasites and bacteria but if its a question of starving to death, its worth risking imo.
Fin erosion can look like fin rot.It can be from nutritional deficiency from the parasite issues your fish probably had..Once eating again that can heal. I would not use meds at this point for it.I would consider a salt dip if the margins appear inflammed.
As for your water..You can raise that tds up if it makes it easier to do frequent water changes..it may even help with the fin issues by giving more minerals to the fish to use. I just didnt want to see you focus on the waters parameters here and miss out on the key issue which is enticing the fish to eat.
Hth,
Al