Your tank is cycling again. After your filter broke and was taken out, it likely killed all or most of your beneficial bacteria. Treat it like a normal cycling tank. Use Prime too, that should help protect your fish a little bit, but may not fully.
You have too many fish in there too. A ten gallon isn't big enough for neon tetras to begin with, but since your beneficial bacteria isn't colonized enough yet, it cannot handle the amount ammonia being put into the water. Some bottled bacteria, like from Stress Zyme+ may help even it out after a time, but it's going to take a while for it to convert because the fish are adding too much, and the tank is cycling. Do heavy water changes daily, about 40-50% or so.
You have too many fish in there too. A ten gallon isn't big enough for neon tetras to begin with, but since your beneficial bacteria isn't colonized enough yet, it cannot handle the amount ammonia being put into the water. Some bottled bacteria, like from Stress Zyme+ may help even it out after a time, but it's going to take a while for it to convert because the fish are adding too much, and the tank is cycling. Do heavy water changes daily, about 40-50% or so.