HP 20/700 - Manual (Page 171)

170 DLT Drives and Tape Cartridges Appendix A
Using DLT Cleaning Cartridges
DLT drives should only be cleaned if CLEAN NEEDED displays on the tape
library status screen. Only use the appropriate DLT cleaning cartridges. In
general, replace DLT cleaning cartridges after twenty uses. Marking the label
on the cleaning cartridge after each use will help you keep track of the number
of uses.
Caution Excessive use of the cleaning cartridge can cause unnecessary
wear on the drive head. The tape library operator panel will
display a message when the cleaning cartridge needs to be
replaced.
See DLT Cleaning Issues on page 172 for information on troubleshooting
common cleaning problems.