I don't think you're overstocked but your'e approaching capacity. It's normal to have rises in toxins temporarily when adding fish. The bacteria have adjusted to the bioload in the tank; when you add more fish the bioload increases and it can take a bit of time for the bacteria to compensate. Just do pwc
as needed until the tank settles on its own.
What kind of danio do you have? Also I believe the Glass Cats and Khuli Loaches do best in groups of at least 5 each.