yes says one tsp for every 10 galAre you adding dechlorinator to the water ?
using the liquid kind+1
Are you using a water conditioner dosed to the size of your tank (not amount your changing)? What are you using to test your water (liquid or strips)? Is the tank cycled? Some more info will help us to help you better!
he was kind of slugish and keeping to the bottomDid the fish show any symptoms?
about a month others seem ok usually they die right after i add water or do a water changeHow long have you had the fish? Could it have been the natural end of its life? Are your other fish feeding ok and seeming healthy? Sorry for all the questions, but we don't have much to go on.
city water and no water sofenerDo you have city or well water? Is there a water softener system or filter system on your home?
80f is the tempAre they tropical? If so are you matching the temperature?