Most likely, the main issue is your filter, not the lens. A 680nm filter can still pass some visible deep red/orange light, and if the filter quality is poor, even more visible light may leak through. That weakens the classic infrared “white foliage” look and makes the image behave more like a deep-red photo than a clean IR one.

One community test showed a major improvement by replacing the Zomei 680nm filter with a higher-quality Hoya R72/720nm filter, using the same camera and similar settings. That strongly suggests visible-light leakage from the original filter was the key problem.

A second factor is that some Canon DSLR sensor stacks remain somewhat less sensitive to IR even after hot-mirror removal, so a filter that blocks visible light more completely becomes even more important.

Also, many dramatic digital IR images are heavily post-processed. White balance alone often isn’t enough. Software like GIMP or Photoshop can use channel mixing and black-and-white conversion to emphasize bright foliage.

So: use a better-quality 720nm IR filter first, then experiment with post-processing. A deeper filter may help reduce visible contamination, but based on the answers, upgrading from the Zomei 680nm to a high-quality 720nm filter is the most supported fix.