Question
1. Filter.
I'm planning to dig my own pond back of my house.
The pond size 9ft(L) x 2ft (W)x 2ft(D) .
How to build a inside filter that actually works within the pond? If possible I thinking using one pump rather than two. Pls advice.

2. Foamy bubles.
Currently I have koi fish using fiber tank.
I have about 14 koi's in this tank.
All of them is less than 1 feet long.
The fiber tank 3ft(L) x 2ft(W) x 10' (D).

Everytime I have noticed that i am getting foamy bubles on the surface of the pond each time I replace the water. Anyway it will dissapear after 2 to 3 days.

Fyi, I do have filter which I wash it whenever I replace the water tank.

If it could be caused by bacteria growing in the water, even if I change the water ?

I hope you could able to answer my question with drawing for the filter.

Thx.

Answer
Hi there!

Why not use an outside filter?
It could be turned into a nice little waterfall, that would not only make it look more natural, but would also oxygenate the water. More oxygen in the water means less harmful bacteria.
You can also use some water plants to help you clean the water.
Do not plant them in soil! Use gravel instead, so that they will have to take all their nutrients from the water.
You could also incorporate a little stream in your pond.
In Nature, a stream acts as filter, as the debris gets trapped between the rocks and is digested by colonies of bacteria on them.
A combination of all of these things would greatly reduce the need for a secondary pump.

Now, regarding the second question, you say that the water is foamy when you fill the tank and it goes away after a few days?
Where is this water coming from? From the city, or from a well? Please let me know.

If you send me pictures of the place I may be able to help you better in designing your project.

Keep in touch!

Carlo