I just tested the water in my 30 gallon cycled tank for the 1st time in a few weeks and got an ammonia reading of 0.25. I had a 0 reading for months!! I immediately cleaned the filter, did a 50% water change and vacuumed the substrate really well. I also treated with Prime right after and will continue to do so each day until its gone. Water tests as follows: Ammonia 0.25 Nitrite 0 Nitrate 10-20 ppm (so hard to tell the difference on chart but healthy either way) Not sure how this could have occurred other than possibly overstocking the tank. No fish have died or acted stressed out, in fact they have been acting like one big happy family. So my question is, am I overstocked? Here is the current stock/size: 1 swordtail - 4 inches full grown 1 dwarf rainbow - 2.5 inches full grown 2 bosemani rainbow - 2.5 inches not full grown yet but will be moving to 55 gallon at 3.5 inches 4 dwarf red platy - 1 inch full grown 7 cardinal tetra - 1-1.5 inches each almost all full grown 2 julii cory catfish - 1 in each max 2 inch Based on my calculations that is less than 30" total and with the bosemani being moved in a few months while some of the others grow a little more, i thought i was fine. Maybe I just hadn't cleaned the filter and vacuumed the substrate well enough in the past month???