Would keep the water changes to every other day but also based on the results of water chemistry numbers.
Don't add anymore salt. Post some pics to see.
The temp at 78-80 is a good range for bichirs. Need a new heater. A temp of 70 isn't good and can result in a slow acting fish. That needs to be corrected asap, like today. Go to the store and get a heater.
High temps are used for ich treatment. Otherwise shouldn't use heat for treating infections. Some bacteria and infections become a problem when done.