Usually performance problems with SQL Monitor end up being caused by a poorly-performing SQL Server - the main culprit is the disk subsystems on virtual machines, because SQL Monitor does many bulk inserts the the write speed on virtual machines is typically sub-par. If data is queued for insert and the SQL Server cannot process it fast enough, that is when you see the memory of the base monitor service bloat up.
Additionally, the initial data burst you get when you add servers is sometimes more than the service can handle, so if you are adding servers to a new SQL Monitor installation, you may want to add one server, let it settle down for a few minutes, and add the next one.
I'm guessing you aren't adding a whole lot of new servers all the time - is this on a virtual machine?
Andy Campbell Smith
Red Gate Technical Support Engineer