I am more referring to the enhanced ball check valve that you have on top of the duckbill. The duckbill should hold up to the acid fine.
Further, attaching the pump to the acid tank like you have it will corrode out the internals of the pump about 6x faster than normal. You need to locate the pump away from the tank.
I didn't attach the pump to the canister–it came that way from Pentair! The system is the Pentair IntellipH. The the motor and pump are separated from the acid tank by an fully-enclosed plastic chamber, so the acid and/or its fumes do not contact the motor or pump.
Not sure what "enhanced ball check valve" you are referring to in the injector. As far as I can determine, the "duckbill" is the only check valve device in the injector (Stenner part #UCDBINJ).