http://www.aaaheatingandcoolinginc.com/importance-of-the-pre-filter/
"No matter how advanced an air purifier is, it needs to have a pre-filter. The pre-filters are built to capture particulates floating in the air that are bigger than 5 microns. But why do we need an air filter if these particulates can be easily trapped by a normal filter? To protect the filters and help them do their job properly. The filters built in any air purifier are built to trap much smaller particulates than the size of 5 or 10 microns. While they will of course trap particles that the pre-filter catches, relying on the air purifier to catch them can significantly reduce its efficiency and limit its effectiveness."
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http://homeairguides.com/about-air-purifiers/what-is-a-pre-filter/
"Function of a Pre-Filter
When comparing different air purifying products, you’ll discover that some devices include a dedicated pre-filter, while others combine this feature with an Activated Carbon filter.
Regardless of how the pre-filter is outfitted on the device, one thing remains true – the purpose is to act as the first line of defense in order to capture the largest particles possible.
If the pre-filter was not on the device, then the True HEPA filter would take too much abuse from larger particles and wear out faster. This would result in you having to spend a lot more money each year in filter replacements.
Pre-filters are perfect for capturing large debris such as hair fur, dust and some pollen. Once these particles are trapped, the other filters inside the air purifier can work at maximum levels."
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Those aren't specific to hydroponic carbon filters but you get my point, not using a pre filter will reduce the life and efficiency of your carbon filter.