Stabilizing tempature and humidity

Hello I just set up my new 4x4x6 grow tent. I have a 600watt grow light. It’s about 18 inches from clones. I have a adjustable ballast. It’s on 75% light. Light set on 18hr cycle. I have a fan blwoing in top duct. There’s ducting going from light to out tent pushing hot air out. My room temp seems to be about 77-81 with humidity at 30-34. I know temp little high and humidity low. How do I stabilize them both. After watering my humidity bis 70. Light is off for darkness hours and heat dropped to 61. Help!

You have a pretty big temperature swing from lights on to lights off. You might need to use a heater while in the dark period. 81 degrees with out C0-2 is at the top of the heat range for me.
A jump in humidity after lights out is an environmental norm. Keep the fan going for an extra half hour after lights out and while the temperature is dropping.
A jump in humidity after they are watered tells me that they are maybe not being watered frequently enough and your plants were thirsty… I don’t think its detrimental.
Humidity is ok at thirty percent. I have had humidity down into the twenties and had not suffered. I just made sure my plants were well watered because they dry out quicker in relation to low humidity.

Happy growing