Casting a non-actor in a lead role is always dicey. At best, it can bring a certain freshness to the screen while leaving the audience unburdened by any associations with prior movies. But when it doesn’t work, as in the fatally unconvincing lead performance of Adrian Mancinelli in Dino J. Gallina’s Red Tide, it can prove disastrous. Mancinelli stars as Alex Nikoladis, a newly released convict, returning to his maritime Florida hometown and hoping to go straight by pursuing a life as a sponge diver. But his plans are frustrated when he comes to live with his brother, John (Josué Gutierrez), who is not only working for a drug dealer and struggling with an Oxycontin addiction but has also managed to lose the family boat. Alex’s efforts to get his brother sober and to make a living for himself unfold in a series of scenes that too often feel like an afterschool special—Mancinelli’s line readings are stiltedly insistent, while Gallina feels the need to underline the drama with obtrusive music cues and, in the climactic scene, a dismal, deal-breaking use of slow motion.