Irregular Shapes Square or Rectangular Area = Length x Width Volume = (feet) Length x Width x Average depth x 7.5 gallons Volume = (inches) Length x Width x Average depth ÷ =23 gallons

Circle Radius = 1/2 of Diameter
Area = Radius x Radius x ð (ð = 3.14)
Volume = (feet) Area x Average depth x 7.5= gallons

Pond Volume
Divide the pond up into circles, squares or rectangles.
Add the divided parts together.

Once you have figured out your pond gallons, using appropriate Pumps and Filters will help

A healthy koi pond should not have any rocks or gravel in the pond itself. This is a haven for bad bacteria, eventually turning the entire pond system toxic. The optimum environment for koi is a recirculating system that has good filtration, both mechanical and biological. It is essential to backwash or flush the filter twice a month, using pond water. Tap water is never used to “clean” the filter, and it’s media.

The pond water should be tested weekly, for ammonia, nitrite, and nitrate, while it is going through the process of establishing the bio-filter. After the bio-filter is established testing once a month is sufficient.

Koi do not have a stomach.  Feed smaller quantities more frequently for better nutritional absorption. Feed only as much as the fish will eat in about 3 to 5 minutes. Koi pellets should be fresh and used within three months to prevent oxidation of the food.

Adding water plants can help keep the water clear of microscopic algae. They provide shade to the pond and compete with algae for the nitrates in the water. Larger koi over 10 inch, love to eat water plants, and can do a lot of damage to them. 

Daily Maintenance
You must prevent dust, fallen leaves, rain and sand from falling into the pool.

Any detritus or mulm which accumulates at the bottom of the pool should be removed. Once every 2-3 weeks clean the filter. Using pond water to flush filter media. Take care not to overfeed. 

Koi keeping supplies:
Fish net
Water filter 
Water conditioner
Food
Ammonia test kit
Nitrite test kit
PH test kit
Salt meter

It is very simple to keep Nishikigoi if you have equipment for filtering and cleaning water. It is advisable to consult a Koi dealer or specialist as to which type of filter is most suitable for you. The most important things to beware of are:
Overfeeding
Overstocking

KOI STRESS:
Koi show stress by blushing red in their fins and on their bodies. When they are handled in a net you can see the red in their fins, between the spines. Also when they are in a stressful environment, such as bad water, they will often show a red blush on their bodies under the scales. Sometimes they almost look like they have varicose veins.

Water Quality:
Water Quality is the key of the Koi health. Make sure your water levels are good, and your Koi will grow beautifully.