The cycle of phosphorous in the ocean is vastly more complicated than what happens in our tanks, and biological processes are only a part of it, though they are a large part. The ocean has many billions of times the volume, billions of times the substrate surface area (made of many different materials than just aragonite sand and rock), and interactions between deep and surface waters that you just can't replicate in an aquarium. The ocean also cycles P on spatial and temporal scales that make drawing comparisons to reef tanks tenuous. Just like our tanks only capture a tiny sliver of the reef, they only capture a sliver of the biotic and abiotic processes as well. What happens in our boxes is sort of analogous to what's relevant to or happening in a 3 foot square patch of sand with some rocks sitting on it in exactly one spot of one reef, which is not even representative of that ecosystem as a whole, let alone the entire ocean.
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