where i live the RH is always high in the summer 70%-90% (i live within walking distance of the atlantic). if your on a tight budget, like myself, and 65%-70% is the highest you've seen the RH. then i'd suggest a DIY dehumidifier. like i did with my growroom. now, i use a small space, only 6sq/f. i would not suggest this for a larger growing area. but if you, like me, are growing in a smaller space, then a simple 5 gallon bucket filled with charcoal, can be effective and really really cheap. as opposed to buying a 200$ dehumidifier.
not only will the charcoal reduce your humidity in the room(takes a few days to notice a change), but it also traps odors. im not saying it will remove the smell of mj, but it will slightly reduce it. replace the charcoal every 6 months, and no the charcoal will not be wasted. you can still use it on the grill when it has ran its course in your growroom