I just got nitrites appearing about 3 days ago. I had about 1.0PPM showing up. Then I went to my LFS got some dirty sponge water to seed my filter with. I just went over this in my head and have a really bad feeling about this. Now my Nitrites have all but disappeared with no Nitrates showing up. The water barely changes a shade but I compared it to my tap which always tests at 0 and I can barely tell it's just a tad different. Any ideas why this is happening? (I'm keep ammonia level 2-4 in my tank.)