In my case...
1. Negative pressure vented display tank upstairs with a four inch flexible duct pulling air out of the canopy and using a Panasonic inline duct fan located in the basement fish room . There is a fan blowing across the tank for cooling purposes and lots of hot wet air gets taken into the vent. Because the air is hot... the humidity in the canopy says about 50% or lower.
I have both AC and DH in the room below, and initially tried to DH and cool all the air in the fish room, but, found that it was too hot and both the DH and AC were running constantly.
2. Now... that canopy air gets blown outside (200 cfm 24/7) out of a vent in the fish room in the basement and fresh air gets pulled right into the fish room. The fresh air coming into the fish room keeps the CO2 in the room down and bumps my tank pH up a bit.
3. With trial and error I found that just dumping that hot wet air outside greatly reduced the run times on the dehumidifier. The tiny window unit AC runs 24/7 is the summer.
This system works great in the winter, the cold air that gets pulled in to replace the expelled hot wet air gets heated up when entering the fish room, taking up the moisture so the DH barely runs at all. My winter utilities were lower than expected.
The system does not work so great in the summer. The air that I pull in is also hot and sometimes wet, so, the AC and DH run quite a bit and my summer utilities are higher than expected.