Here are my parameters:It would be good to know what type of substrate you have, your pH, your hardness, and your alkalinity. You may be seeing a mineral precipitate.
pH: 7.5
NH3/4: 0
NO2-: 0
N03-: 0
KH: 6 drops (API) 107ppm.
NOTE: yes, the nitrite test was done correctly, each bottle was shaken for 30 seconds, then added to waste sample and sat for 5 mins....the filter media that does this is called Nitra-Guard.

What can you tell from that?