Building a 100,000 gallon dream tank is not out of the question compared to Arapaimag's 50,000 gallon tank in that a 100,000 gallon tank would only be a few feet deeper and a few feet wider then Arapaimag's 50,000 gallon. This is due to the square cube law. Such as a 180 gallon fish tank is only two feet longer and six inches wider and six inches deeper then a 75 gallon tank.
I'm sorry. Was going to pass but then decided to reply. I don't know the exact dimensions of the 50,000 gallon tank, but I think 36 x 19 x 9.5 is a close approximation.
Let's clarify to how easy it is to add a "several feet" feet here and there to that tank. Let's use 4 feet = several.
A tank that is 4 feet extra on all dimensions (LxWxH) from the 50,000 gallon tank is:
1) 100% more expensive for water, electricity and mediciation
2) 100%+ more expensive for feeding (assuming it's larger to hold more or larger fish)
3) is 55% more expensive in concrete, tiebars, construction labor since it uses 55% more materials
4) is 34% more expensive in real estate since it uses 34% more land area
None of this addresses the biggest issue. If the tank is 47% deeper (14 versus 9.5 feet) then it's either 4.5 feet deeper into the water table which is ridiculously more than 47% more cost OR is 47% higher which requires virtually a purpose built house since buildings are not typically built with 14 foot ceilings. Moreover, the "extra" 4.5 feet is either farther below the viewing panels (which makes it's extreme extra expense a dubious gain) or the panels are taller which multiplies their cost by many, many times over the cost of the original panels.
Purpose built houses are extremely expensive because they are not desirable to most buyers and use materials that are rarely if ever made. 8 to 10-foot ceilings mean that manufactures make 8 to 10-foot items. 14-foot ceiling means you are likely looking at special orders.
Of course one could get around the added depth issue, by moving the tank dimensions from 36 x 19 x9.5 to 52 x 27 x 9.5, but then again, that would require double the floor space and again likely require a purpose built house. The other problem is getting a zoning license.
One could of course build an add on, or at least try to. The problem is that getting a zoning approval to add on 684 square feet (36x19) isn't remotely the same as adding on 1,404 square feet (52x27)
There's a reason we don't have 12-foot tall ceilings, 10-foot tall refrigerators, 3,000-watt microwaves, gas ovens that can hold 3 turkeys at once and TVs that are 7-feet long that cost just $400. It may seem like an extra few feet is no big deal, but it is when you have to pay for it.