how tightly can we cover our tanks, without effecting oxygenation???

[Magnum Man36 150]

so, the bulk of my tanks are open topped, maybe 1/4 have a cover, but most are set up so terrestrial plants can grow out of them… but my 3 season porch tank, I want sealed tighter, to limit evaporation during the dry winter months… I would assume that if we are using an air pump, we will get oxygen from that, but I believe the bulk still comes from surface agitation… my outside tank currently has custom cut plate glass, that fit precisely into the recess in the frame, I do have the 2 back corners pretty tightly cut off so there is barely space between the frame and the glass for an air line, and a heater cord… without those cuts, the air pump would have to force air out under the glass to relieve the pressure, so that warrants the question of how tightly can we seal our tanks, with out dramatically reducing the ability to oxygenate the water???

 

[Rusty_Shackleford35 150]

I believe there has to be some opening to let atmospheric oxygen into the aquarium. Surface agitation will help with the gaseous exchange, but where does that CO² go if your tanks is sealed tightly?
CO² is heavier than oxygen which means it will sit there just above the surface of the water unless there is an opening to let it escape and let fresh air in.

 

[TwoTankAmin30]

I doubt one can seal a tank completely without making some major alterations. They how do tou deal with feeding and maint.

From day 1 all of my tanks had had decent lids. The goal is not to prevent gas exchange to but to limit fish exiting without permission and to minimize dust etc. from the air settling on/in the water. In many of my tanks the lights sit directly on the top glass. I do not use land plants with roots in tanks. When I was cranking out plecos their tanks had no lights on unless I needed to work in the tank. Only ambient room light or what cam in via windows was available.

I cannot imaging working in tanks or catching fish with a mas of roots from land plants in the way and difficult in getting to things I needed to be able to manipulate. I want clear access to as much as possible via the top of a tank.

Since I want back to using floaters which multiply faster than convicts or live bearers, there area a couple of tanks where I have to remove the floaters to a bucket so I can work in the tank.

It would be extremely difficult for any filter to do its job if we wanted to seal a top so it cut of all gas exhange potential. If it were possible to do and one used air powered filters you would likely pop a tank the way a balloon exploded when it gets over filled with air? More likely it would prevent the air from getting is as the internal pressure would be greater than what an air pump can generate.

I think of one wanted to seal a tank lid to the prevent gas exchange one would need help from NASA to make it happen.

 

[Tomsfish15 58]

There are many examples of sealed ecosystems on youtube. Most do them in jars.
If you have live plants then all things should balance out to some degree I imagine.

 

[Magnum Man36 150]

so I wasn’t implying about silicone sealing a glass lid on, more likely just a tight fitting heavy glass lid, that fits tight into the frame recess, as has been slightly discussed the bulk of the oxygen comes from surface aeration, the bubbles do little, and if there is a limit to the exchange of atmosphere air in the tank ( that fraction of an inch of air at the very top
of the tank, under this glass lid ), and that space ends up with less oxygen than what is normally there, the fish are likely to suffer… so, even though we don’t like evaporation, reducing that to a minimum may oxygen starve the tank???

 

[WhistlingBadger32 14]

I suspect it would have to fit very tightly indeed for CO2 and oxygen not to diffuse from high concentration to low. Add to the fact that you've got a constant inflow of fresh air from the bubbles, and I don't think you've got anything to worry about.

 

[Magnum Man36 150]

I would guess the fill line ( air thickness at the top ) may make a difference… between a 1/4 inch air gap, and an inch and a half, is a significant volume difference…

since I have American Frogbit in this tank ( it’s larger ), I will likely have at least an inch of air, for the frogbit to stretch it’s legs???

 

[GaryE]

With very tight tops, I've noticed a lot of floating plants die. I keep my killie tanks well covered due to leapers. Duckweed could survive anything, but other plants suffer from condensation.

 

[Rusty_Shackleford35 150]

With that outdoor tank I would worry more about condensation dripping from the lid onto the frogbit. Most floaters don't like wet leaves.

 

[Uberhoust]

I only keep a couple of spaces near the cord for the heater, and the intake and outtake lines for the filter, approximately 150 cm2 / 18 in2. I keep the water within a half inch of the covers, the outflow from the filter pulls air along the surface so it keeps well aerated. I don't keep floaters but my Vallisneria americania (not sure about the species) does well with the majority of its blades resting on the water surface. I would like to keep an open top tank, with floaters, but when I do the RH in the house climbs up quickly leading to water marks on the wall.

 

[TwoTankAmin30]

Most of my tanks get condensation on the underside of their lid(s). I have to tilt a lid either back into the tank or into the bucket for tank water for media rinsing sitting near the front of the tank when I take it off of a tank. I have been completely overrun by frogbit in all my tanks where I have put it. All have lids with minimal serious open space. but they are also very far from being sealed to any degree.

It is impossible to have a hang on power filter without an opening for the return water.

Also,

Air contains vastly more oxygen than freshwater, with ambient air being about 21% oxygen (roughly 276,000 mg of oxygen per liter), while fully saturated freshwater holds only a tiny fraction of a percent (typically between 7 to 14 mg of dissolved oxygen per liter depending on temperature). [1, 2, 3, 4]

and

Where the air and water meet, this tremendous difference in concentration causes oxygen molecules in the air to dissolve into the water. More oxygen dissolves into water when wind stirs the water; as the waves create more surface area, more diffusion can occur. A similar process happens when you add sugar to a cup of coffee - the sugar dissolves. It dissolves more quickly, however, when you stir the coffee.

 

[Back in the fold1]

What ? You worried about smothercating your fish ? Won’t happen . The air pump puts oxygen up the wazoo in there and besides all that you can’t seal it perfectly anyway . Seven of my nine aquariums are sealed as tight as I can get them to protect against jumpers and my Betta’s aquarium is so humid air stays in there for his labyrinth . Fret not thyself .

 

[MuddyWaters1]

so I wasn’t implying about silicone sealing a glass lid on, more likely just a tight fitting heavy glass lid, that fits tight into the frame recess, as has been slightly discussed the bulk of the oxygen comes from surface aeration, the bubbles do little, and if there is a limit to the exchange of atmosphere air in the tank ( that fraction of an inch of air at the very top
of the tank, under this glass lid ), and that space ends up with less oxygen than what is normally there, the fish are likely to suffer… so, even though we don’t like evaporation, reducing that to a minimum may oxygen starve the tank???

If you have an airstone in the tank, the oxygen will fill the space at the top, giving the surface agitation more of it to work with. All my tanks have fairly tight lids, although not as well placed as yours. That thing is nice- but I would expect that if you just put an airstone in just to be on the safe side, you'd be good to go. Outside in the winter that air will be cold, so it'll work against the heater, I reckon, but if you have a good enough heater, or add 2 in there to lighten the load on one...

 

[Magnum Man36 150]

air comes from my fish room air pump, in the house, and comes through the wall only a couple feet from the tank, so minimum exposure to the cold

 

[TwoTankAmin30]

You folks do understand that an air stone does not help to oxygenate the water by the bubbles releasing air into the water. The bubbles need to be in contact with the water way longer. The Google AI actually gets it right when I asked "how deep must an aquarium be for air bubbles firsing from the bottom to put air into the water before the bubbles reach the surface?"

AI Overview

An aquarium can be any depth because oxygen transfer happens almost entirely at the surface when the bubbles pop and agitate the water, rather than while the bubbles are traveling through the water column. [1, 2]

How Oxygen Actually Gets into the Water

• • Surface Agitation: Rising bubbles lift water to the top, where it mixes with air and absorbs oxygen. [1, 2]
  • Minimal Direct Transfer: Very little oxygen actually diffuses directly from the inside of a rising air bubble into the water, regardless of how deep the tank is. [1]
  • Any Depth Works: Even in a very shallow tank (just a few inches deep), an air stone successfully oxygenates the water by breaking the surface tension. Deeper tanks just require a stronger air pump to push the air against the water pressure.