Previous study demonstrates that partisans perceive in-party news outlets as fair, and out-party news outlets as unfair. However, much of this study relies on one-shot designs. We create an ecologically valid design that randomly assigns participants to news feeds within a week-long online news portal where the balance of in-party and out-party news outlets has been manipulated. We find that sustained exposure to a feed that features out-party news media attenuates Democrats' beliefs that Fox News is unfair, but the same is not true for Republican's perceptions of MSNBC's fairness. Unexpectedly, repeated exposure to in-party news did increase Republicans' beliefs that Fox News is unfair. This study updates our understanding of partisan news effects in a fragmented online news environment.