I have been given a 60L fish tank. I have cleaned it out with warm water. bought gravel (rinsed and added) filled the tank with water added filter, plastic plants and ornaments and tap safe turned on filter and it looked beautiful after a day my friend bought me a heater so I could have tropical fish
heater has been on for two days now and almost as soon as we had put it on the water went cloudy
My guess is one of two things- either tiny bubbles caused by the change in temperature, in which case it will sort itself out or it could be a bacterial bloom- it'll clear up as the filter grows enough bacteria to cope. Have a read of this, it will explain all about bacteria in fish tanks and how to do a fishless cycle (don't put any fish in before the tank is cycled!!!).
Or it could also be dust from the gravel but I would have thought it would be clear by now.