It's a strange one. Java memory increases non-stop (around 5Mb a sec) whenever I'm looking at my oyster farm (2 rows of 6 oysters). Having sand inside seems to make it a bit worse. I've spent some time fiddling with it and I don't think it's any mod interaction issue.

Screenshot attached (minus piping which I removed for testing).

Yeah this isn't your fault, Oysters were badly done in earlier versions, I've completely rewritten them in 1.2, along with a lot of things to be much more performance friendly. It's too much of a change to fix in the current version though.