Goldfish Tank Trouble

[Linway]

Hey all,
About 5 years ago I got a goldfish in a 25L tank at first he was fine etc.
About 18 months ago I finished university and went travelling so I gave the tank and the fish to my grandparents. Today I've just been to visit my grandparents and the fish is huge! Like stupidly big compared to the little 1inch guy that I bought lol.
Anyway he is too big for the tank so my grandad was speaking to a neighbour about putting him in their fish pond but I was worried about the temp change. My grandparents house is always hot, they have the heating in the house on almost 24 hours a day every day so generally the house is around 24-25oC which has obviously led to the tank being the same temp. Now the fish isn't struggling in the tank with anything other than size so he is happily acclimated to this higher temp.

I spoke to my usual LFS and both said putting it in an outdoor unheated pond at this year will almost definitely kill it.

So what would the best thing to do be?
I'm not sure I can convince my grandad to buy a new tank and I certainly can't afford to do so. The fish isn't ill or anything he's just big. He's still lively and eating fine it's just the size and my grandad does water changes every other day.

Cheers guys.

 

[HHH]

Ok well its good that he's going to go to a bigger pond but does the pind have any fish in it? i dont think just one fish will be enough to die from ammonia posioning since its a whole pond. I dont know how cold it gets where you live but i highly doubt it will be cold enough to kill your goldfish. they are coldwater fish after all. ive had mine live even after the whole pond froze over with a good 4 inches pf ice. depending on how deep the pond is ypur fosh should be fine as long as the whole pond doesnt freeze over.

 

[fluttermoth]

It is a bit late in the year to be putting it out now, yes.
 
It's great that your grandad is doing all those water changes; the'll be what's kept the fish growing
 
What size tank is the fish in now? Would a large plastic storage box be bigger? That would tide him over until the spring when he can go out to the pond.

 

[Linway]

Ok well its good that he's going to go to a bigger pond but does the pind have any fish in it? i dont think just one fish will be enough to die from ammonia posioning since its a whole pond. I dont know how cold it gets where you live but i highly doubt it will be cold enough to kill your goldfish. they are coldwater fish after all. ive had mine live even after the whole pond froze over with a good 4 inches pf ice. depending on how deep the pond is ypur fosh should be fine as long as the whole pond doesnt freeze over.

 
It's not a case of the fish dying due to ammonia or anything. It is an established pond and he would fit in great there. The problem is the temp change. The fish would be going from a constant 25oC water to a maximum of 10oC through the day and colder at night so even a long acclimation would be troublesome to him as he has always been in this temp range (20-25, 24-25 for the past 18 months).


 

It is a bit late in the year to be putting it out now, yes.
 
It's great that your grandad is doing all those water changes; the'll be what's kept the fish growing
 
What size tank is the fish in now? Would a large plastic storage box be bigger? That would tide him over until the spring when he can go out to the pond.

The tank now is an Aqua-40 which is 25L cube tank (not tall, not long just a cube).

I think what I'm asking most for would be something like what you are suggesting as in a larger tank type object that he could thrive in until the summer. The problem is my grandparents are very particular about the way things look so just sticking him in a random box would upset the way their kitchen looks so they wouldn't agree to it lol.
Do you know of anywhere online I could possibly find say a 40-50L thin plastic tank like object (cheaper than glass) that would suffice for a while. When I say cheap I mean less that say £20. So basically something that would still look ok as a tank where the fish can be admired etc but not so fancy that it's costing a lot of money to purchase?

Cheers guys.