Ah...that driftwood of mine is no more...it was rotting!!!.
My nitrate values were sky high the whole time, even after 55% water changes. I don't have fish or any other decaying stuff. Then my attention turned to the driftwood.
After it's removal everything seems to be getting better. No more foam on the water surface, nitrates going down.
I had the same thing happen to me, every time I would clean the tank I would siphone it and remove it with my hand. After a couple of times doing this it all went away.