Shit sorry to hear mate I know the feeling I have many many well established tanks and always keep them clean. Few weeks ago I went out to get some crickets for the beardies not an hour later I got a phone call from the mrs who had just got in from work. Fish were fine when I left but when she got home my jags and oscars were at the top of the tank gasping for air and my red tail shark was dead. It was that quick Turned out i think was ammonia outbreak. I got back an hour and half after I left a perfectly clean well established tank had turned cloudy as hell and was poisoning my fish. 3 hours I stood there pulling water out and keeping fresh going in. All was well after thanks god but just goes to show you it can happen whenever and to whoever at anytime
