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Please do not ask me the "why" for this question, I am not 100% sure myself. I just brainstorm.

I know that metals are usually a NO-NO for aquariums - because they can release oxides and other stuff which is harmful for the living things inside (especially fish).

However, I think that not all metals are the same. I guess that gold should be safe (even though expensive, of course; I refer to pure gold, not cheap alloys). Stainless steel comes in mind too.

Now, does anyone have experience using stainless steel in the aquarium for any purpose? Which kind of stainless steel is better suited?

I am not a specialist, and I have in mind the following categories: general purpose, food-industry grade, medical grade. Of course, I might be wrong about my assumption.

As a "practical" use, is it possible to build an aquarium made of stainless steel? Maybe keeping one side made of glass to have it transparent?

Updates:

  • I did not think of welding, I have in mind using silicone for aquariums;
  • I have fresh water aquariums in mind.
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Salt water vs fresh makes a big difference.

Stainless, both magnetic and nonmagnetic, is satisfactory in fresh water with one reservation. Non-magnetic, eg 302, 304, etc, will be sensitized at welds, particularly spot welds and this permits corrosion of the weld heat-affected-zone. About 50 years ago the standard construction was a spot welded 302 frame; over years these welds cracked because of corrosion. Stainless will corrode in salt waters.

Nickel alloys are great in fresh or salt water, except Monel. Lead is also good in fresh; I have used lead weights on plants for 60 years. Aluminum will corrode but will not hurt fish. Any copper alloy can be toxic.

You could build a stainless frame for fresh water if you use stabilized alloys such as 321, 347, etc. There's a little more risk using the "L" grades. There is no such thing as "food grade" or "medical" grade stainless, only the grades they typically use.

Historically, plain steels were used; steel will corrode, so small tanks (such as 5 gallons) had no metal top edge, and instead used a "bulb" edge (rounded glass). Personally, I had a 50 gallon tank that was 52" long; the top edge steel was badly thinned by corrosion so I added an adjustable steel brace at the center. I assume normal aquarium water with pH between 6.5 and 7.5.

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    This answer contans errors,you need to take the PH into consideration as a low PH will dissolve metalls into the water the same will salt.
    – trond hansen
    Jun 29, 2020 at 16:35

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