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
its very white cloudy iyswim
what have I done wrong and how can I sort it?