rising waters

I just don't get it, my tank water rises by itself.

I do a 20% water change on my 66g and I stop filling before the water line reaches a DIY glass shelf which holds up part of my glass cover. I then do my usual maintenance and when I'm finished, it all looks fine. About an hour later, the water level has gone up and touched a portion of the glass cover so that I can see it from inside the tank (drops below the water surface). Several hours later and more of this glass portion is now underwater. Either my aquarium is shrinking or the water level is going up. After several hours, the waterline stops rising and stays high, slowly dropping from evaporation until the next water change.

I know I'm really opening myself up to some snide comments (and yes, I already know that I'm somewhat crazy), but I have watched this happen many times and cannot figure out what the mechanism is. The water is from my well, so it's under higher pressure and has more dissolved gases in it (which is normal for well water). I've been using it from my tap, so it's somewhat softened and at the right temperature (if that makes any difference).

So water expands its volume when it outgases ? If anything, I would expect the result of outgasing to be a net decrease in volume, but I'm chemistry-challenged, and all I remember from physics is that liquids can't be compressed (which apparently isn't correct).

The fish are, um, peeing?

NEVER hold your staff in front of the tank and say 'part the waters'.

Contrary to common belief, fish is actually peeing, but it can't pee more than the water it takes in, so I doubt this would be the reason

I guess it's 'Tsunami' !

Hmmm, trust you to come up with a question that probably has no known cause

You say the water you use is under higher pressure and contains dissolved gases. I don't even remember doing chemistry at school so here's a real stab in the dark which I don't even understand myself. Could it be that the gases become undissolved in the tank and/or maybe uncompressed and therefore expand the water?

Oh well, I tried

cheerio

Does the water temperature change from the time it goes into your tank and the time the water level rises? The only other think I can think of is that your filters are stopped temporarily, hold water, then discharge more than they use when restarted. Denise

Gather more data points. Test in a liter sized beaker, so you can tell precisely how much the volume changes. Also, weigh the beaker of water at various stages along the way.

I don't think water temp has anything to do with it like someone suggested because 1) you said the temp is matched to the tank, and 2) everybody would be having this problem if it had something to do with temperature.

If the well water is outgassing then that could be your problem. Take a glass bottle of coke and note the liquid level. Shake the bottle, stand back a little, and open the top. What you see is outgassing of dissolved gasses in the liquid. The volume of the soda expanded rapidly in that case, and apparently much more slowly in yours. Another way to think of it is if a gas bubble forms in the water when there was none originally, then the total volume of the liquid/gas has to increase. You should mark a glass of water and then check it again in a few hours. That way you see whether it has anything to do with the tank itself.

I don't know why/how the well water would be offgassing slow slowly. I don't know much about that. Let us know what you find out!

A good shot, but not likely.. dissolved gases in water that are under pressure will release into the atmosphere once the pressure is removed. And of course, water itself is uncompressible.

My question to NetMax is... when he is observing the glass from under the water, is his head *IN* the tank?

Couldn't resist...

If it's an acrylic aquarium, it could be flexing from the extra weight. Even glass can flex a little bit, and maybe that slight movement is causing the glass shelf to drop. Also it would probably be a good idea to check the stand and make sure it's not moving or allowing the aquarium to move. I once had a large glass aquarium break because it wasn't supported evenly. The stress built up in the glass, and one day the front made a loud noise and cracked all the way down. Talk about a mess.

Although I'm no expert on well water, I do know that water from a deep well can have lots of dissolved gases, which stay in solution for several hours. In fact if your aquarium did not have any dissolved oxygen gas, the fish couldn't live. Still it seems like the water volume would tend to shrink as the gases evaporated. Do you have some kind of aquarium decoration that may be holding the dissolved gases and expanding?