In my experience the below happened to work, but as always, your mileage will vary...
Once you know that your hygro is at least close to accurate, and assuming you have space in your humi, I would make some credo's out of the wet florist's foam, load them up with PG solution (just distilled water if that's all you have), and stick them in the humi. Then carefully track to see if your humidity increases. Once it gets to where you want it to be, take out the homemade credos, and monitor the humidity again, if it drops too much stick in less credos, or a smaller one. For my situation, my coolidor ended up needing two 3x3x4 blocks of foam in a tupperware...one coverless, the other covered with holes punched in the top. If both were without covers, the humidity would be about 73%, with one covered, 68%. You may need to fine tune the size of your credo to get it to where you want to go. For me I found that the total surface area exposed to air is what helps to regulate the RH, as well as the use of PG solution and/or beads.
Now if the humidity is still too low with all that, I would say try to seal the humi, or just get rid of it, and invest in a nice cooler...my 2 cents.