Indoor "pond"

Okay, so after having found out that I was reading my tests wrong, and
going back and redoing them, I've found I did indeed have high ammonia
levels for my poor koi.
I've spent the last two days trying to figure out cheap ways of building an
indoor pond (it's winter in canada, apply whichever stereo-types you wish
) and came to this conclusion:

Canadian Tire sells a product called
Simple-Set Translucent Pool Package, 12 ft. x 30 in.
and it includes the pump. It's roughly 1300 gallons of water, and the pump
moves between 500 and 1000gph.

I figure since it's approved for use with small children, it ought to be
safe for my fishes. That is to say, it won't leech any evil plastic
chemicals, or do any other unhappy, unexpected things.

I've also been 'researching' complaints about this product. The only ones
I've found that relate to keeping fish (I don't care if small kids can't
sit on the side), are that the upper ring often deflates. I mostly expected
this since I've never seen a rubber air containing device hold air for very
long, be it beach-ball, or air mattress, or one of those stupid airplanes
you inflate and hang from the ceiling, only to have go limp a day later.
If that becomes too much of a problem, I'll just slit the top open and
stuff it full of styrofoam or something.

Can anyone think of why using a tub like this would be a -bad- idea?

TIA

And sorry for the crossposting. Last time I posted to more than one aqua
group without crossposting, I got yelled at

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