Surprised you're still getting burping with the standpipe. How much flow are you getting? I'd hate to see the salt creep after a month of that much turbulence 8O Any 90 degree bends? If so could they be replaced with 45?
The PVC should extend into the sump water and should be vented somewhere. Preferably, right before the drain line goes into the water, insert a Y so that air can escape.