Might want to consider lining the inside of the tank with styrofoam insulation. Most if not all toilets sold (up here in Canada at least) are pre-insulated and we used to be able to buy kits to insulate the inside to eliminate tank sweating. The stuff I have in mind is denser material than the regular sheet styro-foam though as it is more apt to flake and possibly clog your pump. Another option is to insulate the outside of your reservoir. Possibly do both.
I’ve never seen the stuff used on the inside of a toilet tank, but there is a dense black foam insulation available that you may be able use. Check with a few refrigeration suppliers. Years ago when I was working in commercial hvac work we would insulate the evaporator bundle on centrifugal chillers to stop sweating.
As for getting the humidity down you’ve really only got two choices. Increase your air volume to get more air changes, or seal the space and use some form of mechanical cooling to dehumidify the air.
I never thought to ask. What is the dew point of the air you are drawing into your tent? If you’re pulling air in that is so moisture laden it’s dew point is above the surface temp of your reservoir, it’s not going to matter how much air you’re pulling through, you’re still going to be kinda buggered. You really have to look at the temperature of anything that moisture is condensing on and go from there.
Right dew points are in the 70s and res is 66 to 68 so of course that’s the reason. But insulation may help as stated.
But dehumidifier will lower the dew point. Just by how much is the question.
Watch bargain finder sites local buy and sell sites etc also local rental company’s rotating inventory! A couple weeks back got a smoking deal on a commercial dehumidifier like new only 800 hrs for 200.00 bucks !
I’ve struggled for several grows using small home dehums with poor results buy a beast that takes 10 gallons in 24 hrs out of the room ,trust me once you’ve had to toss a whole crop due to mould even if it costs a grand it’s money well spent !
You might look at the option of sucking fresh air from outside the barn into your grow space you’ll run the risk of bugs and pollen put a good filter on the intake should slow most unwanted creatures getting sucked in ,also can be done with the extraction air as well get it completely outside .The plants should love the c02 rich outside air also.
At the moment, there are many latest dehumidifiers available in the market with trending technologies.
Different dehumidifier provided by different agencies has their own features. You can differentiate the types of dehumidifier and check their reviews here. Best Dehumidifier for Basement.