How long has the tank been set up? Is the cycle finished? What are your current water parameters? When you say you just got new filters do you mean you just replaced the media with new media or you replaced the entire filter? Sorry for all the questions.
Could be a bacterial bloom? Most likely caused by your new filters, keep an eye on the water parameters! It's probably too late to say but when adding a new filter you should always run it with the old one for a while so it gets chance to mature, whilst the old filter still takes care of business.
