Hello, I have had this 10 gallon tank for about 9 months now, and in the past few weeks, I have lost a higher than normal number of guppies. I have tested the water several times and have 0ppm of ammonia, nitrite, and ~20 ppm of nitrates. I have lost around 3 or 4 in the past two weeks and none of them had the normal symptoms that I would check for (nothing in outward appearance other than off swimming, they were not skinnier than normal nor bloated and they did not have any skin or fin issues). Today, another female guppy seems near the point and this is how she is swimming and looks. Thoughts? Thanks much. I don't have a ton of experience diagnosing problems, and I dosed the tank with API general cure after the second guppy died.