LOL CHILDAWG i can see how you would think that and how SPINNER would think that but its true SPINNER we are jsut trying to help you save some of your fish b4 they all die.
you can have like 1 oscar in that tank, at the max for his life. if you want to keep all those fish you will need at least a 150g if not more. you need to get rid of some fish if the LFS' will take them back. that pike if its a Crenicichla lepidota (pike cichlid, 2spot pike or comb pike). they get like 13" he will need at least 75g by himself.
you also need more filtration.
do what CHILDAWG said and go to freshwater newbies and read on the fishless cycling.
I would do a thirty to fifty percent water change so no more fish die. Do it every day until you take the fish back. And like Childawg said read up on cycling in the newbie forum. Hope you keep coming back for more help because anyone of your fish would make a nice single specimen in that tank. This is a great place to get some ideas. If your fish are sick and covered in white spots I doubt you will get any money for them but do the fish a favor and take them back anyway. If you do not feel comfortable in being able to heal them, return them read up and start over or all you will have is a tank full of dead fish.
I assume that ammonia, nitrite and nitrate levels are within acceptable limits? If not;
First thing to do is to carry out a 40%-50% partial water change.
And if it is ich and only IF, You have to treat your tank with the appropriate medicine. ( it should contain benzaldehyde green) Raising the water temperature to 30 degrees C (if the fish can tolerate it) for a few hours every 2 or 3 days will help too.
What I would like to know; Did you perform a regular partial water change during those 6 months. And if so, how much did you change and with what frequency.