Photo's too bright on slow shutter speed with Nikon D3100?

I can take slow shutter pictures at night with no problems, see the link below


I could take a picture like that just fine by lowering the ISO to 100 and putting it on a 15 second shutter speed but if I try to take a picture during the daylight ( of water for example) its too bright

do I need a neutral density filter? if so what type as I'm so new to this

is this okay?

См. статью: Photo's too bright on slow shutter speed with Nikon D3100?