1) Well, there's finrot. The fins and tails are kind of split, not like completely chopped off. It's also quite pale (if that helps). I clean the tank 20% once a week. I just found out 2 days ago.
2) Ammonia: 0, Nitrites: the fish shop staff said it was really good, Nitrates: 20-something ppm.
3) 25 gallons.
4) Juwel Bioflow Filter Super.
5) 14 fish in total. 5 neon tetras, 2 glowlight tetras, 2 albino corydoras, 1 guppy, 1 neon dwarf rainbowfish, 1 hatchetfish, 1 ancistrus and 1 otocinclus.
6) 2 days ago. Water change once a week or if I'm really busy, once every two weeks. Change water 20%.
7) Had the fish for 2-3 years now
8) Nope. Nothing. The tank already has loads of plants and a few pieces of bogwood.
9) I feed them a variety of flakes, pellets and frozen food. Every time I go to the petstore, I get them live food. If I have courgette or cucumber, I boil a piece and feed it to them.