I found something stuck to the filter intake but when i tried to remove it, it floated away. I only see 3 fish. They are zebra danios. I am supposed to have 5, but one is a hider. I'm thinking I should do a water change right away. The meter I have suction cupped to the front of the tank says Live NH3 is at a safe level. This is an ammonia monitor. The meter is by Mardel.