Nice. Thanks. Very helpful.
W13: ...cinder blocks... seems plausible to go that route. im sure an all wood/fiberglass construction would do the same thing tho. Itd b almost a reverse tank if u will, same principles for construction tho.
TBTB: Yes. Of course. And this will get me all the advantages, except the window... ... ... ... ... ... But no $$$ to throw at it. This is a DIY tank but for a professional application. I am just thinking
if at all I can avoid doing the windows because I will have to do them myself. If it was a hobby project, I'd try it. But I need it to be leak proof and leak free and headache free for me for 15-25 years and I am not about to experiment in the spirit of "let me see if I can make it and can make it last", especially never having done a window in pond.
W13: Def. need the "catwalk" above either scenario , kinda cool.
TBTB: That's the simplest but not the only way. A below grade tunnel or an in-tank tunnel can be fathomed.
W13: Personally id prob just get in the pond/pool at that rate but it would make for pretty cool exhibit at ur sanctuary tho

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TBTB: Snorkeling with fish is absolutely the best thing. Again, instead of hobbyist, think professional. Imagine the liability and insurance even if in a shark cage (sad to what our world has come to - people do not want / forgot how to take responsibility for their actions and the risk they know they are taking). It's financially prohibitive even for multi-billion dollar Public Aquariums, I think, as I've never seen ANY offer it. Only profies go into their tanks.
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Weight calculation:
A cubic well of 8'x8'x8' has a volume of 512 cu ft = ~14 cu meters = 14,000 kg water displacement.
To reach neutral buoyancy one would need 14,000 kg of, for instance,
-- iron, density ~8,000 kg/cu meter, which translates into 1.75 cu meters of iron = 63 cu ft = 8'x8'x1', that is out of 8' height of the well, 1' would be fully occupied by a solid iron block...
or
-- lead, density 11,340 kg/cu meter, which translates into 1.25 cu meters of lead = 44.5 cu ft = 8'x8'x~8", that is out of 8' height of the well, 8" would be occupied by a solid lead block...
Yea, I'd say this is a bit taxing on the weight cost and realization ... haha
Cutting down the length and width of the well by half to a 4'x4'x8' will cut the amount of the weight by 4 times to 128 cu ft = 3.5 cu meters = 3500 kg water displacement = 3.5 metric tons of weight = 7850 lb.
That sounds ~ impossible.
Suspending the well part way down does not lessen the amount of the weight enough to make a difference and takes away from the concept too much imho.
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The well can be sunken by placing the weight above it, e.g., on pillars, and then cheap material may be used, e.g., sand and rock.