Just drive along Jalan Sg Buloh from Kg Melayu Subang all the way to Kota Damansara. There are some shops there that sells these water feature quite cheap.

mostly water feature. I think koi fish got also one big shop.

I dont think its good to have koi pond at home . Mainly because it increases the humidity which increase the chances of fungal growth .
Even in modern fengshui design strongly discourages you from having koi pond within the house .
then the later is the maintenance and up keep is considerably high . My old house used to have fountain / pool to put turtles and some fishes ... but once the pump breaks down the whole thing becomes a huge pain in the ass . 

Maybe the first 2 - 3 months you would be happy cleaning it but later sure gonna be damn lazy to maintain it.

My recommendations

Have you considered greeneries like bamboo trees etc that helps to absorb toxic , trees that doesnt grow too big ... or too much leaves .

You also can consider digging the cement area and replace it with soil and cover it with carpet grass and have small wooden table / chairs . ( you can find these accessories along sg buloh to shah alam old road )

I have a koi pond in my living area. Its a 10' x 10' x 4' deep and a 3' x 11' x 5' deep filter.
Humidity is not as issue at all as per say by some. Cant say much bout fengsui.
Let me know what I can help.

***edit***
My pond is in service for 4 years now.

Never clean the pond before. Once a month flush the settlement chamber and 6 months once clean the whole filter chamber.
Filter chamber consist of 5 chamber (settlement, brush, brush, bio, pump)

I have a 2" drain pipe in each of my chamber link to the drain, this is in place because I can chose which chamber to drain without draining all the chamber.

I just pull the 2" pvc in the settlement chamber and viola ... all the gunk is gone.

Errr ... once a month flushing of the settlement chamber will take me 15 minutes to flush and another 30 minutes to fill it back up = yeah, relatively easy.

6 month once full filter cleaning is different, it takes me aprox 1 hour to take out all the media eg. brush, bio beads to clean with high pressure jet and put it back and another 1 hour plus waiting time to fill the water back to my designated level. Quite a workout for the weekend for some. 

***edit***
My pond is expose to very limited sunlight (UV). My main door is about 5 feet away to the pond and that's the only way sunlight can penetrate to the pond and my house is facing south. There are some algae build up on the pond wall but just a light green hue, nothing serious as to algae bloom and no string algae.

There some good doing it yourself, you gets to know if there is something is wrong with your pond hence the trouble if was not spotted earlier.
Some parasite might colonize your filter chamber and this could lead to an outbreak which in turns take more of your time to treat or worst ... whole pond submarine turn up side down.

1 hours not that bad la ...