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