You can't use bacteria to completely remove detritus. Matter and energy are proportional quantities, and life on this planet is only 10% energy efficient. Adding some beneficial bacteria to your tank might reduce detritus a little, but a lot of those products are snake oil unless they are used very specifically, and even then they will not eliminate all detritus.
The main issues with detritus occur when it piles up too much, and include:
1) Potential hiding places for parasites and other pathogens
2) Creation of anoxic zones. If you really have a lot of detritus, anoxic zones can form near the substrate, and animals that move through them can be incapacitated and killed.
Whether or not detritus is a source of excess nitrates depends on how old it is. If it's mostly broken-down biomass, then by definition there isn't enough nitrogen left in it for nitrate to form.
Detritus occurs by the ton in many freshwater habitats, but no matter how pretty our tanks look, we could never imitate those systems. We can't match the processes that produce and decompose that inert biomass in relatively small volumes of water; even small ponds can hold around 1,000 gallons of water, and a large pond or a small lake would tens of thousands of gallons. Because of this disparity, it's not wise to allow detritus to build up like that. Every time I've accidentally allowed it to happen, I've paid for it in fish.
And yeah, you should run a gravel vac in there to pick up the detritus on your substrate. Put a chunk of coarse-grade reticulated foam in the business end to avoid sucking up your fish.
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