Hi all, My main filter stopped working overnight, and my airstone pump tube had come unattached from the pump, and have woken up to an emergency! All fish were gasping at the surface, had lost one (who was quite sickly anyway and had been for months, continually treated and was on the mend but no more), I started water changing immediately, but my HMA filter is not hooked up to a boiler so water is freezing cold, I have gradually changed about 8olitres so far, my tank with two external filters is 300l. I have set up HMA water in my normal prep containers and am waiting for the temp to rise before adding more, I don't want to shock them by lowering the temp with lots of cold water. I have also added an extra air pump with air stone, and have placed the working filter outake pipe so it is agitating the surface, I have also added some epsom salt to help with the nitrate overload shock. All discus are looking ok now except for one, my blue snakeskin, he is lying on the bottom and despite trying to right himself just doesn't have the energy, when he does right himself and swim around a bit he spits out lots of (what I assume, or looks like) uneaten food. Does anyone have any ideas what I can do to help him? With the added oxygen and fresh water his colour is brighter, and he is breathing less heavily, I'm desperate to do the big WC but the temp of the HMA water is worrying me. Have tested PH and etc and it's all normal for my tank, the nitrates were very high when I started but are now coming down. I think the level of nitrate just built and built over night and with little oxygen and etc it all went very wrong. There was a strong sulphur type smell when I started trying to sort it out. The fish all look ok now, much brighter and not gasping, behaving normally, all except for the snakeskin, any advice, or if this has happened to anyone else, any help would be much much appreciated. What should I do now?