It’s never happened to me before, but when I set it up this time the water clouded right up. I’ve dumped some special “cloud begone” juice in there which helps for a day or so then the clouds come back. The fish food says it’s a cloud free formula.
Try using some kleenex on your glasses. 
(Runs and hides)
Is this tank in London?
Did you wash the gravel first?
What kind of substrate are you using? I just set up a tank with Flourite a month or so ago and for a while there it looked like the most accurate biotope tank you’ve ever seen - just like a real lake. My boyfriend suggested getting a great big white catfish so that when you’re minding your own business eating your dinner (it’s in the dining room) this horrible white thing could come out of the gloom and look at you every so often.
Eventually that went away.
It could be algae, or an imbalance of chemicals in the water, or even too many minerals in the water. It’s been years since I had fish, but I remember having a water testing kit where you’d scoop up a little tube of tank water and put some drops of this stuff in it. If the water turned a certain colour, it indicated if there was too much nitrogen, etc. In the water. The kit also had drops to add to the tank water to correct whatever the problem was. This kit was invaluable b/c I was always able to catch problems before they turned into big problems. Maybe go to your local aquarium store and see if they have something similar.
Here’s a pretty good site for both articles and the advice of experienced fish forum posters:
Read some articles there, and don’t hesitiate to register and post questions. They were very helpful to me when we had aquarium problems.
Sailboat
Well, the pictus up and died for no aparent reason so I had the water tested yesterday. Perfect. I do have a bit of green algae in there to feed the snails & the algae eaters, but I’ve had a fuzzy green tank in the past with no clouds. I kind of don’t want to strike this tank down and start over, but I can’t think of what else to do. If I kill the algae would that not adversely affect those critters that munch on it?