the outside (female) threads is 58mm. 

Check the "PIR Sensitivity" parameter setting. Set the sensor level to "High" for warm ambient conditions and "Low" for cold weather use. Try setting your camera in an area where there are no heat sources in the camera's field of view. Try to set the camera on a stable and immovable object, ie: a big tree. If the person/animal is moving fast, it may move out of the camera's field of view before taking the picture. Move the camera further back or redirect the camera. 

It's better to buy a cleaning fluid for lens filter. 

I don't see why not, remember that the filter goes on the lens, not on the camera. 

Female threads