Windows 8 64bit say low memory while 4+Gb free

I have windows 8.1 64 bit, 8Gb ram.

My Task Manager shows 49% used ram, but I still get messages like "Windows is low memory, we recomend to close application". It always says that about the application which is not currently active, but uses more memory than other processes (when Firefox is up, it is Firefox, otherwise it's Skype).

So my question is: how to setup threshold or how to force Windows not report about low memory?

Note: even when it has 70+% free it still reports about low memory. Number of application running doesn't metter.

Note 2: it doesn't happen when I start new app. Looks like windows have some memory checker and it pops up that message on regular basis when swap off. It minimizes active apps(games or browser) and show me that weird message.