My sump is an ex-wet/dry, how do I go about designing a baffle?
I would use a couple of thin sheets of acrylic, cut to fit, and glue them with one of the weld-on products. You would want (optimally) the baffles to begin at about the halfway point in the sump, in a **** and weir fashion. I would probably use three, the first would start from above the waterline in the sump and go down to about 2" from the bottom of the sump. A couple of inches towards the pump, I would have a second baffle that is glued to the bottom and comes to a couple of inches below the water line, then after another couple of inches I would put the third baffle in the same fashion as the first.
Since you noted you do not have much space in the sump, you might try the sponge first. If it solves the problem, it would be a cheaper and simpler fix anyway