Hello. I'm needing some advice on my recent fish deaths. I have a 75g freshwater tank, which I started in July of 2016. I have mainly tetras and angels, but I also have a couple of gourami, plecos, small catfish, and 4 giant danios. A couple of months ago, many of my fish began mysteriously sitting on the bottom of the tank an dying within 24-48 hours. I have a large Marineland backpack filter (suitable for up to 80 gallons). After reading about proper filtration practices, I have since added a second backpack filter (also suitable for up to 80g). This added filtration really seemed to help. However, 2 weeks ago, I purchased 3 black angels and 2 pearl gouramis. All 3 angels have died (the first 2 within the first 3 days and the last just today). The gouramis seem to be doing fine, but today I also lost a dwarf gourami, which I have had for over a month. I just completed a water change. Before the water change, my nitrite and nitrate readings were normal. I usually change out the water every 2 weeks. Could I still have a filtration problem? I read an article on here about the power of cansiter filters. One other note, the large black angel that died today seemed to have some frayed fins, yet I never witnessed any other fish picking on it. The other deceased angels' fins looked normal. Thanks in advance.
