I am reading online that the RH during flowering stage should be fairly low. Like 40-50%. My Grobo is staying at about 75%. Any input?
You’re definitely going to want to lower that if you can…
Air conditioner, open windows for airflow, dehumidifier that’s powerful enough for your living space are all good ways to work on that.
Opening the back hatch of the Grobo might be one way to help get a little airflow in there, and also use some fans inside if you don’t already, that will keep air moving when it’s humid.
Opening the Grobo door once in awhile can help to lower it a bit, but if your room is that level of humidity you should probably have a dehumidifier just in general to avoid mold and mildew issues inside your home or apartment!
Defoliating an auto is risky, but getting rid of a few leaves for airflow might be something to think about. The more leaves inside the Grobo on your plant the higher the humidity usually goes. But do at your own risk, and if you do decide to cut some, do only a few at a time… especially if leaves are touching a lot because that will cause moisture to form and possibly some mold issues there once the flowering progresses.
If you run a dehumidifier, it depends on the outside humidity (and temp) but keeping windows closed can help to control that… having them open while using a dehumidifier can counter-act if the humidity outside is higher than inside
In addition to what @pyromancy posted, if you haven’t added anymore fans inside your Grobo now may be a good time to do so. Good air circulation will help, but won’t come close to resolving the potential issues from too high humidity during flower. Keep an eye out for mold, it will look like webbing.