humidity rh

What you guys think? Nitrogen Toxicity? Chronic Thunder Clones in Ocean Forest/Happy Frog mix 25/75, humidity was a little low but is now 50-60%, Temp was in high 70's and I lowered it to low 70's for the past 2 weeks, fans are on and plenty of fresh air circulation. Was feeding 1/8tsp of Earth...

I have a 60x60x120cm tent, with 4 low ryders. All looks awesome, except for the fact that since 2 days, I've been seeing a big increase in the relative humidity. I've added two small de-humidifiers (cheap ones), but no change at all. I can't get a $200 (more expensive, better ...) de-humidifier...