Issue is ventilation and the NIGHT....... I run at 60% most of the time due to cellar and high water table.
70% is NOT defo going to cause issues till near end of flowering if not vented well (and some strains are fine with it). If good ventilation they'll do good. I just increased air inlet and made sure air circulated better. Worked for me 16yrs ago and still works today
Humidity increases at night as this is when your babies transpire most.
Some ppl turn fans off at night which aint a good idea if you have humidity issues. Do you turn them off ?
Alot of people have issues start with humidity if they veg their plants too long for the space provided also, obviously increase in vegative matter equals an increase in humidity.
Water exposed on your table aint the issue.
@60% You should be able to lower it slightly without changing much about your growroom. I had to lower mine from 80%+.
I found Dehumidifiers useless.
As was pointed out above.. what is your external humidity... if fans aint helping maybe it's because the humidity is 70% externally so you are pumping in at that.
Personally .....as long as you have air movement and new air coming in I wouldn't worry too much at 60%... if you see issues put plans into place to resolve. As I said I run at 60% and rarely get mold issues, but I do try to lower a little towards end of cycle if surrounding climate allows.