Water changes may help with the cloudiness but if your ammonia and nitrite readings are OK there is no reason to panic. The cycle is still going strong as long as the chemistry stays in line. At 8C you have the tank at a temperature where goldfish start to have very low metabolic rates. My first guess would be overfeeding, although it would not seem like it. The low metabolic rate means not much need for food. I would start by cutting the feeding in half and see if that helps clear the water. Your tank temperature is close to the value where people with ponds stop feeding altogether for the winter.
