Hi Carlinraine, If you can't cover the light coming into the house, perhaps you could cover the back and sides of your tank with something opaque. You can buy lengths of plastic that is intended for this purpose from the local fish store. It usually comes with a plant scene on one side and plain black or blue on the other. This won't work, of course, if you have sunlight reaching your tank from all directions.
It might help to just cover your tank during daylight hours for about a week. Don't turn the lights on at all.
As well, if your tank doesn't have any real plants in it, it might help to throw in some big bunches of wisteria or perhaps hornwort. Those plants grow quickly, don't have to be planted into substrate, and soak up nutrients that algae need in order to live.