HITH

hi everyone i hope u guys are fine.i having some trouble with my Oscar fish. at first i thought he HITH as he wasn't eating properly and lost his appetite so i showed it to the vet. he said that these arent holes they are sensory pits. however when i came back from a holiday i noticed that he has small holes that weren'tisible before but he is eating normally (much better then before) so wanted to see i its HITH could u guys please help. i got a medicine for him its called AQUADENE. here are the pictures of the Oscar and medicine.
so guys the questions i have are that will this medicine work and is it hole in the head?
thankyou

OK guys what does this look like. he didnt have these before but he didnt eat well but now he does and eats normally i dont think we get pristine water in Pakistan. so wont this medicine help. guys any other cure. what does this look like to you. ive also notes white spots on a baby flowerhorn. but they just keep on changing. first they have hole then they don't have these white spots and then they just vanish over time. between i have see my oscar scrubbing itself against the gravel
could this be a injury?

dont have water testing kits in pakistan so, i can just guide u with the other two questions
around 6 foot by 24 by 24. fish oscars 8 inch,flowerhorns 3 inches,parrot ciclids 5 inch, 2 green terrors one is 5 inches and the other one is 3 inches inches.
i change my water ever week about 50%.. and i have three sponge fliters,two bio filters and one undergravel filter. yeah i know i need a bigger aquarium. but sadly my 8 foot tank got cracked.

i i also got white patches on my parrots and flowerhorns as well. but ive been seeing these white patches since a lot of time here are the pictures