I got home from work last night to find that almost half the fish in my 4ft community tank were dead. I am devastated, especially because I lost my beautiful white/gold angel. The fish were fine the day before and I only cleaned the tank two weeks ago (I normally do it every 3-4 weeks). I immediately did a 30% water change but I'm wondering if there is anything else I can do? I am at work today and I don't have a test kit, so I can't test the water until tomorrow. Should I do another water change tonight?
A bit of background, my tank is an extra tall 4ft planted tank. I keep it understocked (2 angels, 2 small BNs and approx 10 platies) and the same fish have been living happily in there for over a year. I've never had any issues with the tank at all in that time, but I suspect the filter may be to blame. Its an older overhang filter and I think it may have stopped working properly because when I did the water change last night, the gravel seemed dirtier than usual and the water smelt 'off'. I have ordered a test kit and am going to buy a new filter tomorrow. Does anyone have any recommendations? I was thinking of an Eheim cannister filter? I'm so sad. :(