I use two spoonfuls with bedding, towels and underwear on 60ºC with a pre-wash. Mine you, all that stuff is 100% cotton. All the rest goes on 40ºC, but I up the spin to 1200.
Years ago I always used washing soda in the twintub And a dolly blu for my whites Then chucked the hot water on the garden path and step to scrub it The old days