Use arrow keys to avoid the tacks, some tacks shouldn't be avoided though, look below.

DIFFERENT TACKS- (Ones with a + are positive ones that will not damage you)

Grey Tack- most common normal tack that moves at 10 speed normally.

Green Tack+- gives you an extra hit to take, you can only have 2 at once though, has 5 speed normally.

Red Tack- comes in after 225 seconds, has 5 speed and will try to chase you down.

Blue and Yellow Tack+- either slows down tacks or speeds up your bloon.

Pink Tack- is slightly faster than gray tacks.

Baby Blue Tack+- starts appearing after 290 seconds, makes you smaller for a few seconds, black tacks rival

Black Tack- starts appearing after 290 seconds, makes you bigger for a few seconds, blue tacks rival

White Tack- starts appearing after 210 seconds, it will make you invisible for a few seconds, which makes it hard to avoid tacks.