Front hydrulic disc brake keeps going soft I have some shimano disc brakes on my mtb. I have noticed every now and then the front brake lever goes soft. so much so I can't even fit one finger behind the brake lever.  However pump it then I can just about fit two? It seems to keep happening as well. 

What could be wrong
As mentioned in comments you should get the brakes bled. 

Doing it yourself is not hard, and there are many videos on YouTube showing how to do it. Park Tool has some very good how-to videos and articles. Here is the page for brake service. 

Just make sure sure you get the correct kit and fluid for your specific brakes.