How do I stop crawling a seed?

If you no longer want a specific seed to be crawled, you can deactivate it by clicking on its hyperlinked URL in its collection's Seeds tab, then uncheck the check-box next to its status as an Active Seed. Press the Save button at the bottom of this interface and the seed will no longer be crawled according to any regular schedule. 

To apply this change to multiple seeds at once, click the check-boxes next to each in the Seeds tab, then on the Edit Seeds button above them. In the dialog box that opens, toggle the radio button for the seeds' status from Active to Inactive and click the Apply button to make your change, after which none of them will be crawled on any regularly scheduled basis.