Was it an actual shrimp or exoskeleton from a molt?
If the air stone is near the intake, then move it in order to not get air sucked into the filter but if it's near the outflow it should be fine. The stuff floating around could be micro-bubbles from the air stone that are getting dispersed by the filter. Try turning off the air stone for a while and see if the tank clears up.
It can be hard to distinguish between 0 and .25 on the API Kit. Both tests above look like 0 but it's hard to tell in pics. If you're not sure, you can take the top off the tube and put it onto a white piece of paper and look down into the tube (or look at the tube from the bottom); it can be easier to tell whether it's yellow or green that way.