Would it not be more economical and practical to build some kind of enclosure around your tank equipment to separate it from your mechanical room? The enclosure could be vented separately and you eliminate all your issues and concerns. Keeping the whole room cold will only cut back on evaporation but won't necessarily make much of a difference to protect your house.

Exposed cold water pipes and your water meter are probably the biggest targets, every fish room I've seen that shares space with a mech room had corroded pipes. Next is the furnace ducting. But I think the issues relates to more to the type of evaporation, as salt seems to get evaporated as well it will cause damage much faster. Just sealing the room up and keeping it cold may not make a difference at all, better to have air exchanged. Your house air at 50% humidly won't damage anything, it's circulating through the furnace anyway and would damage other things in your house before your electrical panel or other mechanical room equipment.

Keeping it separate is best option but IMO the next best thing is general circulation. Keep the air exchanged reducing the amount of salt in the air, like I mentioned before this is done with a simple exhaust fan and humidistat.

I think typically the heating is the side effect from cooling process. Just like an ac unit the process involved creates heat during the compressing stage. This heat has to go somewhere and for AC units it's exhausted outside, for dehumidifiers it's used to reheat the air. The air gets hotter due to the inefficiency of the process.

That is 100% correct.

Thanks for the reply. I had an exhaust fan setup in there(which is where the duct that goes outside is from) but it didn't seem to do much. Maybe I just need a more powerful fan

Anyone know where in edmonton I can get a 6" exhaust fan? A bathroom exhaust fan obviously won't cut it

You could try Soper's Supply, they deal with all sorts of exhaust fans for both residential and commercial.

Thanks. I bought a 220 Cfm fan from Home Depot. Doesn't seem like much.

Should this be enought? I had a 70cfm bathroom fan on there before

Outlet won't help but if you drew moist air from the room (inlet on your return air) it would condense on the A coil (just like your dehumidifier).

Pretty sure that's against building code

Depends on the room size, I don't know what the regulation for fish rooms is but indoor "gardens" require the air be adequately exchanged every three minutes. So for a room 10x10x10= 1000cf you need 333cfm.