horizontally mounted precision ball valve

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i recently decided to switch the dreaded red sea valve with a precision ball valve. i own a reefer 350 v1 (i believe) and i couldnt get quiet operations. so recently i swapped it out with a whole new set of plumbing.

couple weeks in and now i am finding that it starts gurgling after a couple days of me setting it to a quiet setting. i am wondering if it is because i mounted it horizontally due to space restraints or because of the smaller dc3500 pump that im using...

picture attached if the story seems unclear

 

[Hats_]

oh yea and it feeds directly into a reefmat amd my ato makes sure that water level in pump chamber is constant