Welcome to the forum Moe! 40ppm nitrates is pretty high. Have you checked phosphates as well? I don't know how much reading up you've done, but just so you know straight RO isn't the healthiest of environments. Discus, especially young discus, require trace minerals for healthy development. I would suggest buying something to re-mineralize the water. or develop a formula yourself that would be much cheaper in the long run. There are recipes in the water section. I use only sponge filters. Sometimes I supplement with an old Magnum HOB to polish particles from the water that water changes along don't catch.
And yes, you can probably say bye, bye to your shrimp