Along with the other ideas suggested above you can hang a wet towel with one end in a bucket of water and blow the air from you fan across it in the tent.
RH is one of the most important environmental factors in a high yield high quality grow. The stoma located on the plant leaves open and close based on the temperature and RH of the air around the leaf. If the stomata are closed transpiration is slowed or stopped. Transpiration moves the water bearing nutrients throughout the plant. If transpiration is not happening because the stoma are closed the plant cannot take up nutrients. This will lead to stunted growth and/or nutrient deficiencies. The ideal scenario is to follow VPD as close as possible. I live in a desert and it is nearly impossible for me to hit VPD most of the year. I shoot for and can remain >40% <65% RH most of the year. IMPO 30% is too low.
View attachment 1414680
I realize that cannabis grows better when its grown at a higher rh than 30 percent. But this guy has a humidifier going already and its not helping much.
I was just trying to tell him that he shouldn't worry about the humidity too much then,because good plants can still be grown with rh of 30 %,I've done it so it must be possible. Maybe I could've got an extra ounce or so if my humidity was higher,but I'm not going to stress too much and try to change how I do things over an oz.