Hi, I’m new here. I have a 5 gallon tank with one big, fat goldfish who is about 6 years old - his name is Jaws. We just moved him into this tank from a 3 gallon a month or so ago. I noticed what I thought was waste getting caught in the filter tube, and when I went to clean it out, I noticed that the problem was a lot worse than I thought. This stuff was all over the plants (I ended up throwing them away). I have never seen this before, either from Jaws or my other tank, which is a 36 gallon freshwater. Any idea what this might be? Thanks!