The saying "An Ounce of Prevention Is Worth a Pound of Cure" is a very valid statement in the koi hobby. There are numerous prevention measures a Koi keeper can adhere to all way through the hobby from end to end, and there is only one place to start and that is at the beginning.
By the beginning I mean long term measures, from the very first glint in the eye of the potential Koi keeper prevention must be a very decisive factor. It is first of all advisable to join the AKCA or a local koi club. It is also advisable to read as many books as possible on the subject of Koi keeping, and ask questions from more experienced keepers, possibly visiting their home and studying their ponds and filter systems, considering what could apply to your particular circumstances.
We remove the spade and pick from the garden shed, even at this stage we should think "prevention", where to site the pond, i.e. not under trees or large shrubs, especially the poisonous varieties, most trees shed their leaves in Autumn which would pollute your pond, is it near enough to your house for easy observation, and consider the amount of sunshine per day to allow your fish a certain amount of natural shade from the sun.
Consider walls and fences as protection from cold winter winds, make sure your pond building materials are aquatic friendly, consider the use of wood preservatives on pergolas, pond surrounds and winter covers etc; think from every point of view of the well being of your fish, keeping stress factors down to a minimum.
Once we have decided on the site we start to think on pond and filter design. The main aim being to produce a balanced eco-system regardless of pond size when completed, one exception would be to allow a decent depth of four foot minimum. If your system is not balanced your Koi will by one means or another suffer at a later date.
Main points to observe are filter and pump size in relation to pond gallonage, another bonus is to fit a UV sterilizer in the system to assist in controlling Algae and bacterial levels in your pond, another point to consider is easy maintenance methods so you can easily flush gunge away from your filters on a regular basis, so as not to upset the efficiency of the filters, which in turn alter water parameters introducing another stress factor for your fish to contend with. Try to ensure the absence of all potential dangerous objects in the pond that fish may injure themselves on, consider the lay of the land in case you use weed killer on lawns etc, do not have excessive plant life in the pond so as to deplete oxygen, and do not use toxic substances where air pumps or blowers arc situated. If you must incorporate waterfalls or waterways do not allow access to rodents or birds as they wash themselves for a good reason, they wash to clean off all sorts of toxic irritants or parasites, consequently they all end up in your pond.
When we are happy with our pond in general we must consider facilities, like a hospital tank or quarantine tank, adequate size nets and inspection bowls, you can not hope to do the job properly without the right equipment, obtain a first aid kit in order to prevent minor injuries progressing into something serous. After finally filling your pond circulate it for a week giving time to detect any possible design faults or leaks. Its no good putting fish in the pond if you have to make last minute alterations, be fully prepared for when your fish arrive.
After circulating for a week empty the pond and refill, then circulate for a further week, at this stage if all is well you are ready to accept your fish.
All the aforementioned suggestions are long term preventative measures, to save yourselves heartache at a later stage. You must do everything you can to reduce the possibility of introducing a stress factor. Learn to understand how your filters mature biologically, you will know at what rate they are maturing and whether you are going in the right direction, at this stage we can now consider short term preventive measures, you are in a position to purchase your fish.
One remaining point to consider when you fill the pond the second time would preferably be through a water purifier, due to all the nasties from raw water straight from the tap, undoubtedly in the future you will be doing partial water changes, so again your purifier will come in handy.
Once fish are present keep a regular check on water parameters especially for P.H, Ammonia, Nitrite, and temperature, preferably every day until your filters are mature, then perhaps once or twice a week using your power of observation condition yourself to a regular inspection of your fish. If possible ensure your system is free from all intermediate hosts, i.e. Frogs, Toads, Snails etc who also carry parasites and disease, make yourself aware of early symptoms.
Now we have arrived at on going "prevention measures" flush bottom drains on a regular basis, vac the pond if necessary, keep pipe work clean internally, disinfect nets and handling equipment, use rubber gloves when handling fish as some diseases can be passed on to human beings.
Thoroughly inspect any new plant life added to the pond, be aware of poisonous plant life around the pond.
On purchasing fish take your time during selection, observe the particular choice at length, take note of the present surroundings where the fish are, are they being well looked after ? take their swimming action into consideration, are their fins clamped close to the body, any visible discoloration, are there any missing or raised scales, any frayed finnage, is the fish socialising with the others? look at body shape allowing for male and female differences, clearness of the eyes, is it generally pleasing to your eye, enquire from the dealer what P.H and temperature the fish is used to. Once purchased transport carefully and introduce it to its new quarters slowly, float the bag for half an hour to level any temperature difference, on opening the bag allow a small amount of your water to enter the bag, two or three times in order to even out any P.H. differences. Whilst in the bag apply vacuum salt at 3 ounce to the gallon for approx; five minutes just to generally clean the fish up. Then gently remove the fish from the bag and place it in its new surroundings, taking care not to let any water from the bag escape.
Quarantine all new stock for at least six weeks, after approx one week do a parasite treatment, then gradually start to feed if the temperature is within the guidelines recommended.
Finally you then observe the progress as often as possible and with mother nature on your side you may just have cracked it.