Enquiry received from Nigel:

GOOD DAY
I LIVE IN FLAMINGO VLEI, TABLE VIEW

I HAVE A POND WICH IS ABOUT 3m x 2m x 400mm DEEP.

THESE ARE THE FISH IN THE POND
5 KOI +-300mm LONG
4 KOI +-200mm LONG
5 KOI +-150mm LONG
10 GOLD FISH +-100mm TO 150mm LONG

I HAVE A WATER FILTER & UV LIGHT BUT NO AIR FILTER SYSTEM.
I FEED THE FISH ABOUT 1 SMALL HAND FULL OF FOOD PER DAY.
I HAVE HAD THE POND FOR ABOUT 3 YEARS NOW.
I DRAIN THE WATER A PUT NEW WATER IN ABOUT ONCE A YEAR AND TOPUP ABOUT ONCE A MONTH.
I HAVE PLANTS IN THE POND THAT TAKE UP ABOUT ONE THIRD OF THE POND.
I KLEEN THE WATER FILTER ABOUT ONCE A WEEK, BUT THE WATER STAYS A BIT GREEN, BUT THE FISH CAN BE SEEN CLEARLY.

I NEED ADVISE ON HOW TO KEEP THE POND HEALTHY FOR THE KOI AND SHOULD I FIT AN AIR FILTER.
THE POND IS MADE OF MOUNTAIN STONE WITH HAS A CEMENT TYPE SEALER WITHIN, IT WAS BUILT BY THE PREVIOUS OWNER OF THE HOUSE.
SO FAR I HAVE ONLY LOST ONE FISH IN 3 YEARS AND THEY SEEM TO BE HAPPY.
SHOULD I BUILD THE SIDES OF THE POND UP BY SAY 500mm TO GET MORE DEPTH OF WATER.


My response:

Hi Nigel.

Normally my advice is not to change anything that works. However, 2400 liters is a bit small for a koi pond. They will not really grow in that pond.

Your pond is also overstocked at more than 390 cm in total. The rule of thumb is 160 cm in total for a 2400 liter pond like yours. (3 x 2 x .4)

I would consider to increase the depth because 400 is to shallow for koi and you need more volume for your fish.

You don't get an "air filter" for a pond. I assume that you refer to an air compressor and air stone to increase oxygen. In view of the amount of plants in your pond, I would definitely put an air stone in. Plants consume a lot of oxygen at night and if anything goes wrong with your pump, you will loose fish.the fish might suffocate.