I use Tide Original (previously used Tide Free). I fill it all the way up. I tried today to add a lesser amount and my diapers smelled like pee. I washed them a 2nd time with the usual amount and they no longer smelled like pee. I will stick to a whole cup now.
I use the powder and fill it up half-way to the line 1. I've already read/heard that those measurements are VERY generous. I don't have any issues with stink or cleanliness.
Re: how much detergent - those who use tide free?