There are lots of options for treating the ich and you have received some advice on that aspect. There isa a link to an article that should help you understand ich in my signature area.
The 75 gallon tank needs to be drianed completely and all of the water discarded. The gravel needs to be removed and thoroughly rinsed to remove the chlorine that remains in it. The undergravel filter needs to be removed and rinsed off, try soaking it in a bathtub. If it is a UGF that has little cartridge filters on the riser tubes you can discard those since thery are soaked in chlorine. Any ornaments that you had in the tank when it got the sodium hypochlorite treatment need to be soaked or thoroughly rinsed to remove the chlorine. When anything and everything related to the tank has been thoroughly rinsed and cleaned, you can set the tank up again and start adding filter and gravel back in. While ading your tank water don't forget to add the dechlor. It needs to be added for all of the water you add and I would at least triple the dose to take care of the minor pockets and nooks and crannies that you may have missed with the cleaning and soaking to remove the chlorine you added.
Now a bit of perspective on a gallon of chlorine. At one time I worked at an ocean cooled power plant that circulated 400,000 gallons per minute of sea water through the plant for cooling. Over a period of time, trapped fish would build their populations in the intake bay. The bay was about 50 feet long, 30 feet wide and 20 feet deep. With the flow of 400,000 gallons per minute moving through this area, we would kill every fish in the entire intake bay occasionally by dumping 5 one gallon bottles of bleach into it. The screens we used to keep the fish out of the cooling equipment would collect about 5 tons of fish when we did this. You have used 1/5 of that much in a small volume of static water with no flow to remove it. We are trying to make it safe again for fish when you have added enough to kill over a ton of fish. That is an awful lot of chlorine.
The 75 gallon tank needs to be drianed completely and all of the water discarded. The gravel needs to be removed and thoroughly rinsed to remove the chlorine that remains in it. The undergravel filter needs to be removed and rinsed off, try soaking it in a bathtub. If it is a UGF that has little cartridge filters on the riser tubes you can discard those since thery are soaked in chlorine. Any ornaments that you had in the tank when it got the sodium hypochlorite treatment need to be soaked or thoroughly rinsed to remove the chlorine. When anything and everything related to the tank has been thoroughly rinsed and cleaned, you can set the tank up again and start adding filter and gravel back in. While ading your tank water don't forget to add the dechlor. It needs to be added for all of the water you add and I would at least triple the dose to take care of the minor pockets and nooks and crannies that you may have missed with the cleaning and soaking to remove the chlorine you added.
Now a bit of perspective on a gallon of chlorine. At one time I worked at an ocean cooled power plant that circulated 400,000 gallons per minute of sea water through the plant for cooling. Over a period of time, trapped fish would build their populations in the intake bay. The bay was about 50 feet long, 30 feet wide and 20 feet deep. With the flow of 400,000 gallons per minute moving through this area, we would kill every fish in the entire intake bay occasionally by dumping 5 one gallon bottles of bleach into it. The screens we used to keep the fish out of the cooling equipment would collect about 5 tons of fish when we did this. You have used 1/5 of that much in a small volume of static water with no flow to remove it. We are trying to make it safe again for fish when you have added enough to kill over a ton of fish. That is an awful lot of chlorine.
