Lower the temps in the room/tent to 75F-73F or so.. The hotter the air, the less RH it will hold, cooler air retains RH better..
With a 1K HPS, I would go thru 3-4 gallons of water a day to maintain 55% RH @ 78F (AC set to 78F). With AC set to 75F, using 1.5 gallons a day to maintain 50%RH. Leaf temps 76F-79F.
Isnt that backwards? Cold air holds less moisture. Condensation happens when warm air hits a cold surface because as the air cools, it cant hold as much moisture. Although It is true that as you decrease the temp of air, the "relative" humidity will go up. The amount of water vaper in it stays the same, but relative to the amount of moisture the cooler air can hold, the rh number increases as temp decreases, unless of course you decrease the temp to the point of condensation and moisture comes out.
Ive been dealing with this same issue and ive come to the conclusion that theres 2 options, 1) dont grow in winter when i have to suck in cold air that has almost no moisture, or 2) switch to sealed room with co2. I thought winter would be great because you never need ac, but it doesnt pay off. I have to heat at night even with lights on which uses way more power than ac, and i have to pump 5 gallons of water per day into the air just to hold 50%. Im thinking late summer/fall/early winter is better strategy. Seedlings at end of summer since they dont need high wattage heat generating lights, fair amount of moisture in air. Moving into cooler temps in fall as veg plants mature and start making their own humidity. Flower in early winter when lights get turned up and need more cooling. Air being brought in is dry but the plants are drinking a ton and putting out lots of moisture, also the point when we need lower humidity to avoid bud rot anyway.
Still i think id rather go sealed with co2 and led. Don't have to rely on outside conditions.
