hey - sorry for late reply.
What makes it happen is the lack of good bacteria in the tank initially. I wouldnt panic about that, its quite common and should start to go after 24 hours with some melafix. Its basically that the
"Ammonia builds up I the tank and the nitrogen cycle begins. As the aerobic bacteria establishes itself, it floats through the water creating a cloudy appearance. A “bacteria bloom†can also be caused by sudden increases in ammonia due to overfeeding or excess organic waste and decay . losses of large numbers of bacteria due to power outages or other circumstances can also cause “bacteria bloomâ€. I copied that
When you say wash the filter....why are you washing it and what do you wash it in ?
Only ever wash your filter in old tank water, never under a tap, as the chlorine in the tap water will kill all the good bacteria that builds up in it.
Your carbon filter - is it a black pad / foam or is it activated carbon in a sachet / bag ? I only ask because activated carbon will remove chemicals from the tank during filtration. But once it becomes saturated you must remove it, otherwise it will leak back into the tank. Usually this is a few days.
If its a new filter then all I can suggest is that you take out some of your tank water into something else and clean your pads in that, see if any dicolouration happens. It shouldnt be doing that in my experience.
What type of tank / filter have you got by the way ?
You also could do with a water test kit, a liquid one really. Do you have one, they are only about 25 quid and last ages, it will be invaluable to keeping fish safely.
