I'm on week 3 of fishless cycle. I have a 7.5 gallon shrimp tank. I had an ammonia spike/ a nitrite spike. Nitrites went down to 0ppm. Bit I still have 1.0 ppm of ammonia. Nitrates are at 20 ppm. Does anyone know what is happening here? I thought ammonia was supposed to dissappear when nitrites did.