Nitrite Problem Also

HI, I have a 55 gallon and a friend of my sons gave us his whole collection of mixed africans. The tank was probably only half cycled but we had no choice and had to take the fish now. The ammonia after peaking is now almost down to zero but the nitrites are high. I have been trying a 25% change every 2 days and today and last Wed did a 50%. According to the test Im using the nitrites are still way too high. Checked the water from the tap and almost no nitrites are present. The Nitrates come down after the change. Any suggestions? What is the possibility that the tetra aquasafe I'm using with the water changes is giving me innacurate readings on the nitrite? The fish seem fine, even getting a lot of color back and a few had small ulcers that are healing after I took the salt up to 1.5% Any help would be appreciated.
John