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[APD] Humidity and Open Top Aquariums
Gee, the open top aquarium topic has generated a lot of discussion. I never
really thought about humidity problems before. Claus gave us the hyperlink
to his article. A large part of his article addresses the humidity
and anyone considering open top aquariums should read it. At least you
won't go into it blindly like I did.
Actually the house I am in we bought a year ago. I am in the business of
doing forensic engineering reports for insurance companies. When I saw the
HVAC unit I knew we had some problems, as the whole closet was black. It is
located in the garage, and with the air leaks in the door, the closet was
sucking in 95degF-98%RH outside air. I took some air samples inside the
house and they basically came out OK (no Stachybotrys, Aspergllus or
Penicillium). We got an allowance to go towards a new HVAC unit, which we
had installed after we moved in. We completely replaced the inside of the
We had the AC unit sized to just about struggle to keep the house cool at
about 75degF when it is over 90degF-98%RH outside. That means that the AC
unit runs longer per cycle thus insuring the max amount of moisture removal
from the inside air. It is typically about 73degF-55%RH in the house
throughout the year, including the sun room where the tanks are located.
The sun room originally had just a window AC unit, but we had an HVAC duct
piped into the room since I also use half the room as an office, and wanted
it to always be comfortable. When it is over 95degF outside the sun room
gets a little warmer since it has windows on three sides and a metal roof.
That's when I turn on the wall unit for a few hours in the afternoon.
So it is really hot and humid here in Corpus Christi during the Summer. It
is actually a lot nicer here on the island as we get a breeze from the Gulf
of Mexico. Today was one of the colder days since we moved in. Outside I
measured 55degF and 55%RH.
If you live in the south of the USA or in a tropical humid area, as long as
you have a well maintained HVAC system, I would not hesitate to put an open
top aquarium in your home. Claus's article says that if you keep the
surface area of the tanks to less than 2 % of the room area you will be OK.
He also recommends to keep the water temp within 9 degF of the room temp.
My tanks are actually 7 % of the sun room area. In the summer I might have
a problem if we didn't keep the double doors to the room open all the time.
By doing so the area also includes the kitchen and living room and that
brings the percentage down to 2%. Claus says that if you stay with his
parameters the RH should not go any higher than 5% with the open tanks. I
think if your HVAC system is well maintained you get stand 15%.
If you live in a warm humid area and have an improperly functioning AC
unit you could easily end up with mold problems from the humidity
accumulating in your home, regardless of what type of aquarium you have. If
you live in such an area and live in a house that has a pier-and-beam
foundation where the crawl space is not properly ventilated and the vapor
barrier is old in the floor, humidity can permeate from the crawlspace. If
your house smells of mildew you probably have a humidity problem. In that
case any aquarium will make matters worse.
Up north if the air is dry in your house in the winter an open top aquarium
will increase the humidity in the air and make the house more comfortable.
In NJ we used to put trays of water on the steam radiators to do this. The
question of condensation on windows is really not an issue if it gets really
cold outside. Whether the RH in the house is 40% or 60%, if it gets cold
enough moisture will condense on the windows. However, I would use some
judgment here. In NJ my wife insisted on putting a humidifier in a small
bedroom with the door closed until the window sills rotted out. A storm
window will provide enough insulation to often prevent the condensation. If
in doubt, keep the door open to the room and let the moist air humidify the
rest of the house.
The bigger question to people in the north is what to do in the summer. We
did not have central air in NJ. We used cross-ventilation to stay cool.
However without air conditioning the house can get pretty humid during the
rainy season. So once again use your discretion. If you have an AC unit
an open top aquarium should not be a problem. In fact having an open top
aquarium is a great excuse to have to go out and buy that nice window AC
unit you've wanted for the room.
If you have the cover glasses for the tank, try it open top, and if you
observe humidity problems that you can not resolve, try putting the cover
glasses back on.
As far as plants turning brown and crispy once they emerge, I find that most
plants do this just as they break the water surface. The leaves are
probably not adapted fully to being emersed, and without a waxy coating they
dry out. However, as the stems get taller the new leaves seem to be more
resistant to drying out. I still get a few leaves that dry out, but since
its a biotope and not an aquascape I just say that its natural to have some
dry leaves. Sometimes the plants will grow right into my MH lights where
they should get fried, but it is amazing how well they cope with the extra
heat. Even in humid TX I have a small spray bottle next to the flake food
and every time I feed the fish (all day) I spray the emersed growth. I
can't say how much more difficult it would be up north were it is much drier
the winter, but if you can keep a house plant going, I would think the
emersed growth would eventually adapt. Cindy will have to tell us how she
Also Tom Barr gave us a hyperlink to his design for using PC lighting with
open top aquariums. It consists of some really nice glass end supports.
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