clams

well.... not the the affect that you would notice unless you have a HUGE clam in a small tank (or jsut a bunch of them... but then youd be dosing a LOT of Ca and ALK. haha).
as with corals clams have zooxanthellae in their mantle which is a symbiotic algae that produces the clam's glucose via photosynthesis. as with all algaes, they do need nitrates (fertilizer is basicly this and phosphates) for many parts of their structure such as DNA replication.
clams also have 10X more zooxanthellae than most corals, so the SUPOSEDLY can actualy reduce your nitrates, but you arent going to notice.
 
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