Source 1 is an illustration as stated by the DA author "This is a drawn BG. which I made...". Source 3 is a Premade background which means it was created by the DA author in Photoshop. Both of these sources are not acceptable according to the Rules and Guidelines: 5.6. 3D Renders or Illustrations as Source:
Using other people's 3D renders or illustrations (even with permission and no matter in which form they are offered) creates a false impression of your artwork. So 3D renders or illustrations can not be used as sources, unless they are entirely created by yourself. Don't use an image that has been altered by the source owner nor an entire work created by someone else.

You must replace these sources with acceptable non illustration images.

The link for the Bubble brush shows the search page and is incorrect. Replace that link with this: http://edelihu.deviantart.com/art/Bubble-Brushes-85621024

Consider this a "friendly" warning. You should make these changes as soon as possible to avoid an official warning which would remove your entry from the contest until it is corrected.

I saw the comment and thought I might help, I used the flickr advanced search for images that can be used with modification and found these underwater scenes: https://www.flickr.com/search/?advanced=1&license=1%2C2%2C9%2C10&text=underwater%20scenes

Also check this link: http://www.publicdomainpictures.net/hledej.php?hleda=underwater

When you use DeviantArt stock you have to check that the image isn't a Photoshop manipulation or an illustration. Usually if the description says "premade" it's been created by the DeviantArt author and can't be used in a Pxleyes contest.

I also suggest that when you fix your entry you remove the shadows on the fish and turtle, there wouldn't be shadows when they're swimming in the water.