High Nitrates/Fluval Ribbed Tubes

I posted a thread a month or so ago about having problems with high nitrate levels. The closest thing people could say about it, given my maintenance, stocking level, and feeding regime, was that I had more gravel than needed for my tank.

I just thought of something.

I have a Fluval 204 cannister filter as the main filter in my tank. It has ribbed hoses for the intake and outtake.

I have read about people being disgusted by how these ribbed hoses collect gunk and think that they might be part of my problem.

Does this sound plausible?

And if so, does anyone have decently detailed advice on what I can replace them with?

Thanks!