is 70% Humidity at night a problem

Hi. To answer your question so you understand it..I suggest you look up how stomata vents work. Been at 70% RH in the dark is a norm for me. I've the exact same thing that happens to me. I'll explain why In a way you can get it. But look it up. As plants sleep. Stomata vents close leading to a build up of RH in your tent from evaporation from the soils. A build up in your room will be normal from the exhaust expelling that water vapour. Ideally yes, a lower RH helps a plant in late flowering. As the plant itself slows down a lower RH will stop the leafs vents from having what they need, leading to lager intake of nutrients from the substrate But, is it essential, absolutely NOT. I harvest autos that are held in 65-70% RH. VENTILATION IS KEY to stop from getting rot. I use to run my dehumidifier like mad getting the RH down. I crop I think I spent like 150e on jst keeping the RH low and tbh there was no difference in my bud when I jst increase my ventilation with (fresh air exchange will be vital) so not just expelling the RH from the tent. You'll need to change out the air in the room the tent is in. Oscillating fans will be keep. And a good negative seal. If you've any more questions just shoot me a mes about growing successfully with high RH environments. States in the US and around the EU has RH in excess of 70 and this is were the best seeds in the world would some say come from and are bread. In my own country our RH is at its lowest at 60% and highest at 85 and I've done many grows. 1 I got caught out with a small bit of rot as my osc fan failed. Other than that. Don't waste your money trying to control it. Yes, there is an hr or 3 a wk i have to use my dehumidifier to dry out my grow room. But, trying to keep it at a steady level below 45 when you've 55 there's no point. And as for lights out. Good ventilation and exchange of air in your grow room. Good luck

Yes, it will be a big issue, High RH in flower is the cause of moulds and WPM. you need to keep the extractor fan on at night to keep the RH low. ideally 45-55% RH in flower.

You can have troubles with most strains if they build fat buds, if not during the flowering you will deal with them in the late or driying process. You want to have less chances? buy a dehumidifier and turn in on during night and dont forget to constantly recirculate air inside the tent.

70% promotes microbial growth more than you want. Will you have a problem everytime? Maybe not... But, it'll probably be the cause of issues at some point. bud rot is my guess. This is more of a problem in flower for sure. You can either use a dehum after lights go out, or keep the room closer to 25C (whatever daytime temp is) and the RH% won't rise. Colder air holds less water, so as the temp drops RH% rises. As the plants get larger, thet humidity will only rise further.