What ? A filter is a filter, where it removes large or small particles. Though the in tank "screen" as you call it really does filter out a lot of stuff. Just for grins and giggles why don't you take it off for awhile after you replace the main filter (keep this filter for later) . Then with a new main filter and the "screen" off run it for a month. After a month, replace the main filter and cut it in half. Now compare this filter to the old filter. I did this in Tech School. You can tell us what your results where, then I'll tell you what my results where.