The nitrates are fine if you only have fish, no corals. Sounds like algae so you probably have phosphates, as well. The bug is most likely an amphipod. Bugs is good! They help keep the tank clean. Keep everything in place. You can pull the algae out by hand if possible.
Get some cleanup crew if you don't have any, snails and hermit crabs. They can help tame the algae. Consider using GFO to control the phosphates. Phosban is a good one to use. Small, frequent water changes will help.
Check the source of your water. Tap water can contain quite a bit of nitrates and phospates, my water here runs at around 10ppm nitrates. Water conditioners won't remove them, only an RO/DI filter will. If you have nitrates in your tap water and aren't using RO/DI filters to remove it, you will never get nitrates below your source level no matter how often you change it. If you are using tap water consider buying an RO filter unit or buying water from your LFS.
Get the phosphates and nitrates under control and the algae will disappear (eventually).
If it's any consolation, everyone has algae at some point. Don't give up. I let my phophates get out of hand for about a month and I've been battling the algae it caused for the past six months, but I'm winning. My tank no longer looks like a lawn and is really looking quite nice at the moment.
Patience isn't just a virtue, it's a requirement.
