I finally moved my Studio out of my Bedroom in to a designated Room. (I got the room for free so I won't use another room iven if the basic geometry is kinda bad)
After playing around in the room (l: 5.8m w: 2.2m: h 2.8m) I found a pretty good spot on roughly 35% in all dimensions. (so monitoring position in the rooms is around l: 2m w: 0.7m h: 1.2m) I kinda like the appeal of the sound there.
I have measured the worst room modes: at 62, 255 and 500 Hz I have a fair amount of gain in bass, at 70 and 100 hz I have a huge amount of cancelation in bass response. Higher frequencies and reverberation are not that much of a problem as I have some good amounts of furniture in the room. For early refections and mids (500 Hz) I planed some thick acoustic foam and I use a book shelf for diffusion.
Now I want to treat the room with some bass traps to get rid of those room modes. I read a lot about broadband absorbing bass traps, diy bass traps etc. But I am kinda scared of those materials Rockwool, fiberglass etc. Especially with the manufactured ones, I do not know whats in there an if they got damaged on shipping etc. (I don't drink alcohol, I don't smoke, I don't do drugs... so i kinda don't see why I should places critical materials in my working space.)
Are there any alternatives to those standard bass traps. I read that sand might work?