If both of them died there is something wrong with your water or it got contaminated with something..
List your water condition, temp, how often do you do water changes,do you buffer the water ?Tank size, ect..
With my africans I keep them at 78Degrees,I use 1 teaspoon of baking soda ,1 tablespoon of epsom salt and 1 teaspoon of non iodized salt or sea salt per 10 gallons of water.
I do a minimum of a 50% water change EVERY week to keep any wastes down to a minimum.. The PH should be close to or above 8..
Any other questions just ask,maybe I can help out a bit...