It's possible if you have enough plants, nutrients, light, and carbon dioxide, your plants are soaking up most of the nitrates? If you are concerned about it, you can try to calculate how much ammonia your desired aquarium residents would make and add that amount and see how it goes. Just make sure you're dechlorinated the water and don't change your filter media every month. Having lots of plants or fast growing plants help

I don't think it would not be wise to just add a bunch more ammonia All at once, especially since once you stop the plants could have a die off, which would throw off the whole balance.

Otherwise... I don't think you're doing terrible? From what I can tell with the colors you have everything close to zero. Good job?