Could you post ( I have only looked quickly over the previous posts so you may have done already) - a sketch of the set up including where the items of electrical equipment and their wiring are in relation(including distances) to the aquarium? Also, what voltage is the equipment and what is the electrical supply ie: generator, mains, TT/TNCS/TNS. Where is the water supply which fills it and include the pipework and whether metal or plastic?
The usage scenario and layout, equipment is different at each use, and generally we arrive just ahead of use, and would start to fill the tank as soon as it's loaded into position (baring any obvious safety concerns that would prevent us doing so). Of course this is a very different way of working compared to what most sparks on here would consider reasonable - but that's TV/events. You hit the ground running.
The need for speed is the reason all studios and event teams have on site dedicated sparks to monitor/test/re-arrange in real time. And the sparks will live that life full time.
The water supply isn't really an issue as the tank is filled once, then disconnected from supply. In any case, the supply would be rubber/pvc hose of some form. The permanent pipework between the tank and it's filter system is PVC. The filter system itself is bunded to protect against internal leaks, with all electrical on the outside of the bund. And of course, RCD on board for each circuit, even though it would only ever be fed by a site feed that is also protected and tested prior to each use.
I think mostly in the UK at least exhibition/event venue power to each stand is TNS/TNCS. In studios normally TNS, and when we're in the middle of nowhere relying on generators, TT. Not much help huh?..
I have similar thoughts to you on this but still need to see a sketch - my early thoughts before seeing sketch are to make it a 55V-0-55V TT installation centre -tap earthed and the 110V passed through a 10mA RCD. 110V provided by a safety isolation transformer supplied by mains through a 30mA RCD. Then bond all metalwork together and to terra-firma. OP - this is not a definitive answer.
The industry is firmly on 240v, and this will not change. The specialist equipment needed doesn't exist in 110. In many ways 110v would probably make a great deal of sense as in reality, studios and exhibition venues represent about the most intensive construction environments you can imagine.
Everything else steel in these places will be connected to earth by default. That's certainly standard practice, it's just the tank which makes the sparks stop and reconsider sometimes. Hence my asking on here.
Whilst so much varies the constants are:
There will always be temporary 240v 30ma protected power routed all over the place around the space the tank is in, supplying hundreds of items of equipment for A/V, lighting, cameras, the list would be endless.
There will always be people entering/exiting the tank at times that the surrounding power supplies are needed to remain on.
People will always be in the tank at some point to perform in some way.