Filters and Grainy images

rickp

I was down in the Florida Keys yesterday just relaxing an i took some pictures with my 50D. However most of the images came out somewhat grainy. The one thing I did do that I haven't done in the past was to stack 2 Singh Ray filters, a LB Color Intensifier and an LB Warming Polarizer. As a result I had to increase the exposure and sometimes the ISO, but with the ISO i never went over 400, as a matter of fact I usually shot at about 100 or 200.

So the question is can stacking the filters case the grainy effect if not what could have?
Here are some images
http://www.flickr.com/photos/rickimagegallery/sets/72157624079208536/

Thanks