As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS GROUNDED. RETURN TO DEPARTURE DUE TO BOTH LH/RH FUEL FILTERS CLOGGED. ENG #1 FUEL FILTER IAW AMM 73-11-41 & J/C 33L40073001. LEAK CHECK GOOD. PERFOMED TEST NO.7 ENG IAW AMM 71-00-00 & FOUND NO FAULTS. ENG.1 FUEL FILTER CLOG DETERMINED TO BE CAUSED BY BIOCIDE TREATMENT PERFORMED ON 11JAN2020 IAW AFMM 20.16.3.H. ALSO SEE AALA202001279028.