Yes you can have high ammonia with no nitrite readings. It is likely though the high nitrite readings are soon to follow.
As said above it looks as if you tank may be underfiltered although this may not be the reason for your ammonia spike. I would increase your daily water changes as they are not enough if you are running 50ppm of nitrates
As said above it looks as if you tank may be underfiltered although this may not be the reason for your ammonia spike. I would increase your daily water changes as they are not enough if you are running 50ppm of nitrates