infection

Gday every one just wondering if any one can tell me what has happend to my batch of beer it's 4 days in this is about my 7th batch never seen this before

I fermented 46L of IPA split across two fermenters, and one has picked up an infection, unfortunately. In my 12 years of brewing, it's the second time I've had an infection that required the beer to be tossed out. It's a little more interesting this time in that I have a 'control' as such in the...