How do I know my filter is still running ok? can it wear off in just a month?

1, high humidity will cause filters to not work until they dry back out. Increase your air exchange rate or introduce more fresh air ports in your tent. AC removes humidity from ambient air as well as dehumidifiers. 2, vulcan is not the best of brands for carbon filters that I can see. you really want to be 100-200CFM above your max exchange rate. eg. your fan can pull 500CFM, your filter should be able to handle 600-700CFM 3, you want raw active carbon material in a housing with a prefilter on it, keeps dust and bugs out. The activated carbon pellets should be in a thickness of at least 1.5" to 2.5", if your filter is the black pleated fabric kind, it will not last long. A good carbon filter will last many grows if treated well. good, https://www.amazon.com/VIVOSUN-Australia-Charcoal-Pre-filter-Reversible/dp/B01DXYMBU6/ this is an budget brand of the style you want to get. lower grade carbon inside but does the trick. bad, https://www.amazon.com/Carbon-Filter-Honeywell-HEPAClean-CFS/dp/B01KIMO56Y/ stay away from stuff like this.