Internet Speed Issues

[Xttract]

Hey! I have a problem with my internet that i'm hoping one of you smart people can solve. When no one is using internet and I am on the computer playing online games, I get a very good ping. But as soon as someone in the house decides to watch a YouTube video in quality higher then 240p or begins to download, my ping goes to CRAP! It can't be my router as it is a good one
DSL-AC68U, also should mention I am connected by Ethernet and my drivers are all up to date.
My Current Internet Speed
PING: 31
DOWNLOAD: 4.36 Mbps
UPLOAD: 0.63

My Internet Speed When Watching a YouTube Video At 480p
PING: 272
DOWNLOAD: 2.70 Mbps
UPLOAD: 0.35

Any help would be greatly appreciated!
If it helps I live in Australia (No one I know has this problem where I live, most of there internet is actually quite good)

 

[indyitguy]

Was it always like this? When did the lag start?