Don't know about a performance water screen for the 225, BUT, the intake screens can easily get clogged if you have been running through grass or seaweed. They just bolt on, so unbolt them and inspect carefully.
Another issue is engine height. The anti-cavitation plates should be even with the bottom of the hull at the transom. For every foot of offset from the transom (say, for a motor extension) the anti-cavitation plate should be raised one inch. When running on plane, the anti-cavitation plate should be just skimming on top of the water.
Finally, once the alarm goes off, have someone drive the boat while you closely inspect the the anti-cavitation plates and see if they are both skimming the surface. Your trim meter may be indicating that both are trimmed equally, but one may be trimmed up more than the other due to engine torque, unequal weight distribution, or hull obstructions. I assume one of the engines is set up as counter-rotating.