exciting
i was actually looking into this type of build - not 20k litres though because the heating bill for that is HUGE! and maintenance.
many overseas use under tile heating, but from what i gather, especially wtih a huge tank like that, make sure the room is insulated. Also, maybe incorporate a simple solar heating method with black hoses, you can get this unit for swimming pools.
Heating wtih underfloor heating may be difficult, it will require many KW to heat it.
A friend of mine is a heating/cooling engineer and she said for that volume, good idea to go Gas/water heat exchanger. very efficient and cheap to run - if you have gas in your house already, thats even easier!
FIltration would be easy, you can build in a sump on sides as you said
as for glass in front, if you use glass, it has to be exceptionally thick, that CAN distory color and image and a green haze but it doesnt scratch, acrylic in the other hand, i have heard panaques and plecos scratching acrylic - but lighter and better visibility.
To be honest, for that type of set up, i would post on MFK because overseas, that type of set up is actually extremely common while in NZ its not and our experiences here is not as much.
as for stocking, come on! you hvae to have monsters in there!! :bounce:
a huge tank like that, yo have to have the pacu, aros, giant gourami and anything else that gets huge lol
my next build is a 4000 litre aro comm, not enough large fish in nz to have a truly monster tank IMO! david and i have this discussion frequently lol