GFO will remove phosphate and silicate, but it won't remove much in the way of organics. Some fresh carbon will help remove organics. You might need several batches, if there's a lot of organic content in the water. Unfortunately, we have no practical way to measure that parameter.
When you say "detritus" do you mean leftover food and the like, or some sort of microbial growth?
I'd probably do a few water changes, although they might fuel a bit of growth, to keep the ionic balance in line.
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Jonathan Bertoni
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