well a colony of BB can double in size within a span of 24 hours. I think it is safe to take off one of the filters, but leave the other one running for a good 5 days or so, then take the other one off, and you should be good. a lot of people underestimate how fast the bacteria reproduce. It doesn't take long for the bacteria to spread, it just takes a long while for them to find their way into your tank when you start a cycle.