4KB/sec = 240KB/minute
Which would give ~1.2MB in 5-10 minutes, not 160MB as you're seeing.
Could you double check what you're seeing?
I don't see anything immediately wrong with your code, but, as others have said as well, I wouldn't rely on Windows Task Manager if you want accurate data*. Have you tried using any other memory tracker?
*Anecdotally, my Windows Task Manager is completely broken. It lists every single running application as using 0 CPU and memory.