For an SPS tank, I wouldn't do something as low as 3x. Try to do at least 10 - 15x.
Personally, on my 60G cube, I run about 3700GPH total turnover which is ~62x or so? As long as the flow is dispersed and not coming out like a jet it'll be fine.
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32"x32"x20" Cube-ish tank
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