Different brightness on each level of quality settings

Hello! I have problem. Built a scene with exponential fog on epic quality then set medium and brightness level fell down dramatically. I suppose that it it connected with fog. Scene is kind of night and fog is needed in case of art. I checked post processing volume already and didn’t find anything. If there ant thoughts about, or any existing topics, please helb. At least if there any settings for not to change fog with settings (lock fog quality) please give an info. Thanx so much!