Is my fish tank just dirty or is there something wrong?

[GouramiCory]

Hey guy! So I've been having this problem for a while where this black/green/brown film/gunk keeps covering my freshwater tank's plants, rocks, and glass. It is removable but it eventually grows back but I assume it's also not letting my natural plants grow. (I have a mix of artificial and real plants since my real ones just will not grow. I also cleaned two artificial ones for comparison.) Ever since I have bought my real plants they have barely, if at all, grown in general. Honestly, I have no idea why both these problems are occurring, and under in the substrate there are these long spiky like worms as well. Does anyone know what any of these problems are and is there anything that could help?

I do my water changes every two weeks or so and my fish tanks temperature is at 78 Degrees F. I have added some pictures which includes my parameters. I also have a penguin bio wheel hob filter as well. 

 

Thank you all in advance!

[Fish Folk]

Well . . . the dark greenish stuff might be cyanobacteria (blue-green algae). It's not actual algae, but rather a type of bacteria. You can remove a lot of it manually with pipettes and by hand, but to crush it, you'll need to hit the tank with something like API Erythromycin. If you "sniff" your water, you'll notice a foul odor caused by the Cyano Bacteria. You can try a "black out" where you wrap your tank in paper, and turn off the light for a week or so. Your plants may die, but the cyanobacteria get cut back the way too. It's honestly hard to be rid of. We have it in several tanks chronically It won't kill fish . . . but it does eventually impede plant health. 

No idea what you mean by "long spiky like worms." Got any photos??