When {HEAD ~ the pH} of the fixer solution is below 3.5, formation of hydrogen sulfide gas can be {TAIL ~ a problem} 
When { HEAD ~ the pH } of the fixer solution is below 3.5 , formation of hydrogen sulfide gas can be { TAIL ~ a problem }
OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL