Great work on the height but natural anything is not happening with this so very unnatural human made thing called a lawn. I had to make a living taking care of hundreds of lawns. What a beast and it is anything but natural.
Water...NOT every day. Only ONLY when that grass stays down so you are able to see your footprints. This technique works! It trains your grass to have deep roots to get at the last vestiges of water 4 to 6 inches deep. In between waterings weeds and fungus go bye bye.
This is a fungus no doubt but dog gone if I haven't been able to find it on the internet!
Watering is your problem. Too much water too often. Your mower blades need sharpening. Dull blades shred the tips of your grasses and expose them to disease. Mow once per week even more if possible. Never allow your lawn to get so high that you have to take off more than a third of the blade of grass, too stressful.
Fertilizer is critical for all of the plants we humans plant. Just like water and sunlight and drainage. Fertilizer has to be a balanced formula. (go get Dr. Earth's Lawn Fertilizer...incredible stuff and that is saying something coming from me).
Aerate once a year if not more by pulling plugs out of your lawn and leaving them where they fall.
Every single mowing since you've got this fungus clean your mower blades with alcohol before and after. Collect your clippings!! Read the question/answers on this site about lawn management. Please ask more questions as you learn how to deal with this BEAST called a lawn. Grins!