Rear door heat exchangers facilitate the phenomenal increase in data center capacity. To maintain required cooling performance, these systems must be protected against particulate build-up. To maintain required cooling performance, these systems must be protected against particulate build-up, especially biofilm, sediment, rust and scale which can lead to rapid tube-side fouling and decreased heat transfer efficiency. Precision filtration is necessary to prevent fouling and ensure continuous, reliable heat rejection, specifically targeting oxidized metals and system-generated rust from upstream components.