Hi, Ive recently started a new tank and all I have done so far is fill the tank up with water and Ive left it for about a week as Ive been busy. Ive not started to cycle the tank yet. Yesterday I turned on my lights and I witnessed little parasites? They were on top of the water clinging on with their tales. They are a few mm long. Is it because I left the water without the filters on and the water has become stale? If anyone knows what they are and if they are dangerous to fish that would be great thanks!