I saw some for sale today that were about 2 inch or 3 inch, so I would not be surprised that that one is that big.
I compared them today and both looked the same color to me.
Doesn't look like you got anything in your filter that will take out the nitrates. With the testkit (I have the same) it is hard telling when you are
I was afraid you would say that you wanted the others in pictures. Can only help with the white one and a really bad picture of the grey one with the