Please open a support case on this item.
Without some more information it will be hard to help identify what the problem exactly is. Questions like how many nodes do you monitor? Do you have the netflow module installed? If you do how many flows/devices do you monitor?
Our small implementation with 1400 monitored elements can easily generate 100GB+ LDF file in day. This while our main MDF file never goes past 20GB. We do know exactly though why it happens. We have the Netflow module running and capture all that data.
To combat the ever increasing LDF file, every morning at 6am we run backup on the database. Only on Monday do we do a full backup, otherwise it is an incremental.
We have to do this because this is a generic SQL server limitation (not specifically a Microsoft SQL Server issue). All SQL databases normally log everything. Even if transactions are committed, they still exist in the log usually until a backup is done. Our production servers for in house developed applications create so many transactions that the logs have to be rolled when full which is normally between every 30 minutes to an 2 hours