BigShegergan

Not sure your root color is all due to low oxygen. are you using nutrients that have a brown tent to them. Many times the nutrients you use will stain the roots but if your plants aren't showing signs of deficiency then you should be alright. To me your roots don't look slimy or rotten. The other thing I have found is to cut back on nutrient levels from what is recommended. I have run recommended levels and almost always suffered burn especially in DWC. I think if you were having DO issues then you would see it in your leaves very quickly. Usually with too little O2 your plant suffers with in 12 to 24 hours, but never hurts to have better pumps especially if your going to upgrade to RDWC in the future. Another thing to cool your reservoir that's simple if you have the space is a small fan but it does cause evaporation to speed up and you have to check water levels more. Lastly how full is your reservoir? looking at your pics it looks like it might be over the bottom of your basket. you want the level about 2cm below the basket. just some thoughts, glad to see your plant with the strange leaves is doing well.

Nice choice of strain to grow. It's one of my favourites to smoke or vape. Enjoy the flowering period!