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I looked through the stack exchange list of sites, hoping to find one more suitable for my question, but decided that this was the most likely place to get the answer I'm looking for. I'm not an engineer, but I'll try to explain myself as clearly as possible. Here's the set up: Two fifty-five gallon fish tanks, each on a metal shelf stand. Each tank has two holes (drilled or cut out, idk, and wouldn't mind having the neccessary steps for this explained) in their glass floors. There are corresponding holes drilled through the metal shelves that they sit on. Two U shaped glass tubes seem to hang under it, one bigger than the other, so the smaller one is above it. One end of each is set securely through the holes of one shelf and the holes of one tank, same on the other side (picture to better explain). The idea is that, when both tanks are filled with water, the tubes would fill, too, and the fish would be able to use them as highways, so they could swim freely from one tank to the other. I'm not sure how the tubes could be securely connecting, though I was imagining in the same way that the walls of the tanks are connected (I think it's glue, not sure, clarification welcome). Also, a friend proposed the problem of pressure from the water above being too much on the tubes. I really just want to know if this is doable. And, if doable, but there are some glaring obstacles, to have them explained. Thanks in advance and sorry for disrupting the well-versed engineer-y air of the site. (Side note -just because I'm intruding: This is actually an idea I came up with for a tank set up in a novel I'm writing. I've lived around fish tanks, but have never actually tried doing anything remotely like this with them- not sure how to put that. Anyway, thanks again.)

ignore the upside down fish

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4 Answers 4

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I see three immediate problems:

  • The tubes, and their joints, will experience high pressure.
  • If there is even a slight movement in one tank but not the other, unless the tubes are flexible, or perhaps even if they are, the tubes or the joints will break.
  • Gravel, dirt, etc. will accumulate in the tubes, which will be difficult to clear.

The siphon proposal sounds better, but the tube would soon accumulate air and have to be frequently refilled with water.

If you really want to put holes in your tanks (and risk destroying them), I'd suggest putting the holes an inch or so below the water line. That would eliminate the problems of high pressure, dirt accumulation, and air in the siphon.

Your biggest concern will be how to ensure that the seals are strong and flexible. Eventually someone (even you) will accidentally bump into a tube. You really don't want the tube to crack or the seal to leak.

I was about to say it sounds like an interesting idea, like a Habitrail for fish, and then I googled it and found an interesting fish habitrail video three tanks interconnected by siphon tubes

It uses the siphon suggestion. If you look at the video you can see the air accumulation problem starting, but I think that could be mostly eliminated if you could arrange for continuous water circulation between the tanks (e.g. a common external filtration system taking water from one tank and returning it to the other).

You could make the tubes longer and have the tanks separated farther apart.

It certainly seems like a better idea than potentially destroying two tanks.

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  • $\begingroup$ Siphons loose "siphon" pretty quickly ( one day), one needs a vent at the top with constant suction to get trapped air out. $\endgroup$
    – blacksmith37
    Apr 15, 2019 at 18:21
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This is possible, but the stress concentration around the holes in the tank bottoms will probably cause them to crack and fail catastrophically! Here is an easier way:

Instead of connecting the bottoms of the tanks, simply invert your bent tubes, fill them with water, and place one end of each in each tank to form a siphon. Fish can swim up into the water-filled tube, traverse the gap between tanks, and then swim down and out of the tube in the next tank over.

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  • $\begingroup$ Hmm.. fish have internal organs ("swim bladders") that regulate their buoyancy by changing the internal gas pressure. I wonder if that system would work properly at less than atmospheric pressure while they were in the syphon. Otherwise, your fish might explode... $\endgroup$
    – alephzero
    Apr 15, 2019 at 8:15
  • $\begingroup$ This is no trouble for fish - source: have seen it done $\endgroup$
    – Jonathan R Swift
    Apr 15, 2019 at 9:31
  • $\begingroup$ @niels Nielsen - it's implied that the metal shelf takes the weight, so bottom of tank shouldn't be under significant stress. I like your suggestion because it's more awesome than 'underneath tubes', but not your answer as "probably" is barely ever a good engineering answer $\endgroup$
    – Jonathan R Swift
    Apr 15, 2019 at 10:54
  • $\begingroup$ I used "probably" as a useful way of expression chance of success for 34 years in high tech engineering. It implies a certain amount of experience-based judgement. $\endgroup$
    – niels nielsen
    Apr 15, 2019 at 20:25
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Yes, you can do it by either using flex silicon sealants or some rubber compression washers like those commonly used in copper tubing.

Your supports have to be solid and offer easy access to the bottom for maintenance of the pipes. The pipes on the suspended part have to be supported by strong but flexible brackets.

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It is common for tanks intended for salt water to have holes with bulkhead fittings. The bulkheads normally come with NPS threads in the US. It would be just a matter of connecting them the way you want ; clear flexible hoses would be best. Tanks would need to be ordered with the size and location of the holes specified as it is not reasonable for an amateur to cut the standard tempered glass bottoms. Apparently one would not have gravel in these tanks.

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