Its not the size Im showing you its the color and fuzz..... Look at the picture you posted earlier, some roots are white and some are brown and stringy, and even the white roots are not bright white on your picture
I am telling you that your roots and your plants look exactly like the problem I am having. Your symptoms are just like mine, including plants getting better and worse, and you grow in the same medium as I do. Ive been researching and working on this problem for over a year and growing for going on 13 years. So yes I am telling you that you defiantly have pythium and it is not what you think it is, it is more of a pathogen then a fungus, but I am not going to argue with you over it. You have the answer to your problems right in front of you, take my advice or struggle with it for the next year like I did.