Yes, detritus contributes to an increase in nutrients.
What detritus is is basically dead organic matter that is slowly decaying. It can be made up of proteins, carbohydrates, dead plants, dead bacteria and a list of other things. Detritus used to be alive - so at one point this living thing was taking up and eating nutrients and growing - putting those nutrients into their bodies. Once they die, their nutrients settle and become detritus. Detritus can then be "recycled" as food for corals and filter feeding inverts. However, in our closed systems there is no way to massively recycle these nutrients so a build up occurs. Detritus accumulates deep within live rocks, live sand and even gets trapped in our sumps. During water changes it is especially important to remove as much of the detritus as you can.
Most corals, however, prefer to have a little nitrate and phosphate in the water. Even in nutrient poor zones, such as intertidal pools where most species of SPS (such as acropora) tend to thrive, phosphate levels still range between 0.03ppm and 0.024ppm. That just goes to show how delicate these ecosystems are. If your striving to reach 0.00ppm phosphate, you will end up bleaching and starving most corals. Whereas, if you go above 0.03ppm phosphate you will end up browning out and perhaps killing most species of SPS corals and limiting the growth of coralline algae.
So, while we want things to be as clean as absolutely possible, you will have to maintain some amount of nitrate and phosphate in the water column to grow corals to their full potential and to keep their coloration strong.
A shop vac is a great tool for cleaning sumps. That was a great idea, and I am glad that you have one on hand. I used to do mine by starting it with a powerhead and siphoning it out. That was a headache!
