its hard to tell much from the photos.... ich looks like salt sprinkled on the fish, the saltier the worse. if this is what you're seeing you can usually kick it in the early stages simply by raising the temperature a few degrees.
So, LewisH, how are your guppies now? Any changes? Is the white streaks that are worrying you? Those can be just from a mixed group of guppy "strains" or color varieties of mixed parents.
It's hard to see with the filter bubbles in your pics. Ich can look like that but it's usually smaller specks at first.
