How to make a selection on a 16bit grayscale of only the darkest pixelspixels

[andyseabrook]

So there is an issue perhaps due to hardware limitations and large images that I cannot click on a pixel of pure black, 0, and use Select By Color with a threshold of 1 to create a selection of all pixels between 0 and 1. I need to select all those pixels in the image with shades of 0.7 and 0.9 for instance. And once selected use the bucket fill to make them all equal to 0

Or at least I need to be able to make all of those pixels between 0 and 1  = 0 by another method. So is there another option open to me? How can I achieve this?  

Thanks