As miss wiggle says your nearly there it sounds like your cycle is starting to get back into shape.
Usually you get High ammonia low nitrite at the start, then as your filter media start coping with the ammonia, the ammonia drops and they turn it into Nitrite. Keep up with changes if the Nitrite gets too high again. But what will happen is that your Nitrabacter

? (Bacteria in filter) will start to multiply and then turn the nitrite into Nitrate, which you have to remove with water changes. Once you get to this point, your filter is cycling properly

Obviously when you add new fish, you add more ammonia. So little bit at a time is always wise.
There are some good diagrams online if you search google for fish cycle or something.
Basically its looking good for you, keep your eye on them, and keep up the good work. It is a faff of a process, but you can control all these levels of toxins in your tank with water changes and a good filter. Just remember what miss wiggle said about filter cleaning / changing pads. Manufacturers often say replace every week etc. Personally I think unless you start noticing water output is slowing, dont bother.
Good luck - hope ive helped a bit.
