How Much Dehumidification to out run evaporation?


New member
Hey All,

I have a 90g Reef tank with a ~30 gal refugium. It is setup on an auto top off that runs off my RODI system. My Reef Tank is in my living room, open top.

I run a 70 PINT dehumidifier 24/7, I don't have a way to drain it to a drain or outside, so when it fills up the tank, It shuts off. I have to drain the collection bucket 1-2x a day.

With the dehumidifier running like this, I have not been able to get my humidity under 50%, it typically floats between 53% and 57%.

I assume all I can do is get a larger dehumidifier that would be capable of pulling more moisture out of the air, faster than the tank can evaporate it back into the air? (Anyone have any idea what kind of rate the evaporation is?)

I have seen commercial units with capabilities up to 300 PINTS per day. I don't believe I need one that large? I also have a Dehumidifier in my crawl space keeping the moisture in my sealed crawl space under 50%, so that it is not pulling moist air into the house from the crawlspace. (I think it's like 70% of the air in your home comes from the crawl space or something like that)

Anyway, I am hoping to pull my inside humidity down to about 47% and maintain it there.

Thanks for the help..



New member
I covered as much of my tank and sump as possible (skimmer draws are from outside) which was the biggest factor in evaporation. Went from topping up 5 gallons a week to around 1 gallon/week.

Even with them covered it took my dehumidifier around 3 weeks of running constantly to pull the moisture out of the house to an acceptable level. Now it actually hits the target level and shuts off.

Not sure this would have happened without covering the tanks.

Good luck.

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Vinny Kreyling

Premium Member
I run a big unit by Aprilair & their recommendation is 55% so you are not that far off.
My sister bought a table from the Bahamas years ago, inlaid pattern.
After some time up here it dried out because of lack of humidity. So too dry is not always a good thing. Get a cover & see if that helps enough.


New member
Agree with everyone else. The science shows as you lower the humidity of the room the MORE evaporation occurs from your tank. Your just wasting money on running the dehumidifier at the moment.