Touch wood, not had so much bad luck as you lex.

mine was i had a trigon 350 with rainbows and community stuff and few very expensive L no plecs, my air pump stopped overnight and the outlet for the filter just wasn't enough and i lost most of the fish, gutted.

also i had another frt in a seperate tank from denzel, she was a female and extremely gentle and friendly, she scratched herself and got an infection, i had to inject her with antibiotics twice a day for a week and clean her wound daily, also daily water changes, she didn't make it, i cried like a baby