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Monday, March 28, 2011

New 5,000 gallon pond - Should I put rock in it?

I am building my 1st Koi pond - 5,000 gal. I have done a lot of research and feel I am ready. I have someone who will excavate the hole, and place the liner. He majored in landscape design at an excellent university and has been working for about 7 years. He recommends after the liner is placed to cover the bottom with pebbles, and stack cobblestone sized rocks up the sides to cover the entire liner. This is for esthetic reasons, especially since the pond will be lighted. This sounds like a great idea, but I can't find anything that either recommends or discourages this design. I am concerned about debris getting trapped between the rocks and not reaching the bottom drains. Any suggestions? - Bill


You are correct, the rock on the bottom of the pond will trap debris and it will prevent the bottom drain from working correctly.

Fish waste and leaves will slide across the liner on the bottom of the pond and into the bottom drain, but if there are pebbles on the bottom, they will catch everything.  Koi fish love rooting around at the bottom, expect a lot of pebbles to end up in the bottom drain.

Any rock on the bottom of the pond will need to be cleaned thoroughly on a regular basis. When fish waste builds up and fills the small spaces in between the rock, it creates perfect conditions for anaerobic bacteria to grow: a low oxygen environment with tons of nutrients. Anerobic bacteria release hydrogen sulfide, which is poisonous to fish. Hydrogen sulfide gas smells like rotten eggs and is released into the pond if the rock is disturbed.

To clean the rock at the bottom of the pond, you will need to:
  1. Catch the Koi and place then in a temporary tank
  2. Drain the water out of the Koi pond
  3. Power wash the rock on the bottom
  4. Fill the pond back up and let the water dechlorinate for a few days
  5. Place the Koi back into the pond
To summarize, you can put pebble rocks on the bottom and clean the pond out often, or you can leave the bottom of the pond open and let the bottom drain do all of the work for you.

Aesthetically speaking, algae will cover any surface in the pond.  Both liner and small rocks will end up looking the same after a year or so.  It is ok to place the larger stones along the pond walls.  They won't capture debris and will add to the water scape.

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