We recently upgraded to a 240l tank, we did it all 'properly', water test readings have always been fine. Yesterday the water went very cloudy and the fish seemed distressed. We did tests and everything was normal apart from nitrites which were a little raised but not very high. We did a wter change and the fish seemed happier. This morning it's even cloudier and the fish seem to be really struggling. Will do another water change but what else can I do? Dh has overfed them the past couple of days (despite being told not to) and they are being treated for a fungal infection as we got given a fungussy fish when I bought a few guppiesast week.