[simongo]

Hi,

About a month ago, I installed a cold water aquarium to keep and observe brook trouts at home. To cool the water, I bought an old dehumidifier, carefully twisted its aluminum evaporator (I am not sure if it is the correct name, but I meen the cold tubular element of the dehumidifier) and lowered it in a plastic container filled with water. In the same container, I immerged a long copper tube in witch the aquarium water circulates. It works as a heat exchanger that very effectively cools the aquarium. Until yesterday...

Some chemical reaction corroded the aluminum tubing of the dehumidifier. White spots and accumulations formed along the tube and caused it to puncture and release freon. I wonder what is the reaction and how I could prevent it? Should I use automobile antifreeze instead of water in the exchanger? Or distillated water?

To keep the water surrounding the two tube circuits in movement (otherwise ice was forming around the evaporator) I placed a small aquarium aerator to generate bubbles. Could it have had an effect?

If anybody can answer this chemical problem, I would realy appreciate: I just bought another used dehumidifier and need to find a fix before my trouts die!

Thank you!...

P.S.: Sorry for my poor english!

[enahs]

I suspect it was a galvanic reaction(http://en.wikipedia.org/wiki/Galvanic_series) between the Aluminum and Copper, as a fish tank is a very electrolytic solution.

Do not use dis-similar metals, even if they are separated by what appears to be a large distance.
I would probably use some plastic tubing or PVC to connect the two, and see if that solves the problem.

[Borek]

Either your water is corrosive enough for this type of aluminum alloy (not very likely but hard to be completely ruled out) or it is electrolytical corrosion enahs mentioned. In the second case nothing should happen if both metals are electrically separated. Just because they are in the same water is not a problem, but if they touch each other you may be sure corrosion will occur. If they don't seem to be connected - think it again, perhaps they have common ground or something like that.

[simongo]

Thank you Borek and enahs,

I made some more search on the net and what I found goes in the direction you suggest. There was a contact between the two metals, so I corrected the new installation. And since the copper tube connects at both ends to plastic ones that goes to the aquarium, I am sure this one is perfectly isolated.
And to make sure this won't happend again, I filled the «exchanger» with a solution of antifreeze used in automobile radiators: they contain ingredients that are supposed to protect metals from that type of corrosion.

So I hope it will be OK this time. I will monitor it closely and come back with the verdict in a few weeks!

Thank you again!