Returning it is the best option. Or sell it to a person who has a large pond.
Yea that would be awesome but I really don't have the room indoors and even if i did i think my gf would take a lot of convincing, i wish i had a basement!!
i have the room to go 5'x12' and a lot deeper in the garden if I build a really well insulated plywood/concrete tank but depends on my circumstances over the next few years to if I can build it in time... 
you don't need to heat it just keep the water from getting frozen. The fish will not likely to grow pass 4' in 10 years so you will have quite a bit of time to deal with it.
Yea your probably right but I know its fate probably ends in a 2'x6' at best if I take it back, not to many seriouse MFKs that I know of in the uk and I think tropical ponds will be super rare if there are any because the winter here is cold, I will look tho, I have time he is only around 3" ATM
just keep the water from freezing over and have some surface water area for it to breath since it need to take air from the surface. There is no minimum water temperature for it since water can't go below 0 degree Celsius.
Well that's opened up a lot more options for him either way
thanks
thanks for all of the advice everyone
