Partial water change outs can reduce the amount of anything dissolved in the water but not totally remove it. Although it is sometimes necessary, draining and refilling a pond should only be used as a last resort! Do not use large water change outs to clear green water conditions. A large water change out will normally make the situation worse, not better. Often, several partial water change outs, performed over a period of days or even weeks, can reduce the concentration of an undesired item to acceptable levels without serious after effects. A water change out reduces the amount of a substance in the water by the same amount as the percentage of water replaced. Remember the concentrations of any "good" stuff in the pond is being reduced at the same time as the "bad" stuff. Also the water being used for replacement may have undesired components as well.

A water change out is considered to be when a measured amount of water is drained from the pond and then replaced. Just adding water and letting the pond overflow will not accomplish the desired results unless significantly more water is transferred. Water added to replace that lost by evaporation is not part of a change out.

Example: It is desired to decrease the Salt in a pond by one half. Any of the following will have the same approximate result:

• Seven successive 10% change outs.
• One 25% change out followed by four 10%.
• Two successive 25% change outs followed by one 10%.
• One 50% change out.

Depending on the urgency to carry out the action, the largest number of change outs over the longest time would be the best approach.

Unfortunately, this does not apply in the same way to pH. The change in pH for a given water change is dependent upon the Alkalinity and pH in the pond as well as the Alkalinity and pH of the replacement water. Adding water with a higher pH than the pond water will raise the pond water pH but it is difficult to predict how much. Remember that if the water being added to the pond has a pH higher than that of the pond, make sure any ammonia in the pond has been treated before adding the new water.

It is considered appropriate to change out from 5 to 10 percent of a pond's water per week. A small pond (3 tons or less) should receive the 10% weekly change out. The 5% change out is appropriate for a large pond (20 tons or more). Any water replaced after a weekly back-flush of a filter system or other maintenance actions should be included as being part of the weekly change out amount.

When making the water replacement with tap water that contains chlorine or chloramines, it would be better to pre-treat the water with the chlorine neutralizer before adding it to the pond (particularly small ponds). If this cannot easily be done, use a fine spray of water over the pond and divide the total computed neutralizer dosage into two to four parts and add while the makeup water is being added. Don't Forget To Turn Off The Water! Set a timer or something to remind you that makeup water is running into the pond. Inexpensive flow timer shutoff devices that hook directly on the hose are available and are a good safety item to use.

Final Thoughts

Keep good records of your pond. A chronological log of chemical test results, treatments, maintenance actions, water change outs, and even addition or removal of fish can help determine the cause (and required treatment) of a future problem. I keep mine in a computer file but just a simple notebook is all that is needed.

Keep chemical test apparatus clean. Scrub out the test vials periodically. Just rinsing with pond water doesn't get out all the residue build-up. Whenever you buy a test kit, write the purchase date on it. If not otherwise stated on the test kit, replace any liquid based test kits every year. Replace the sealed packet dry powder and pill based kits every two years. Be careful about anything that you put in your pond. Know your pond capacity and carefully calculate and measure dosages . Know what you are treating for; it is usually better not to treat at all than to dump in something because you think there might be a problem. Second only to ammonia poisoning, more Koi have died from improper treatment with medicines and chemicals than for any other reason.

Many times, the first indication of a problem can be detected by simply watching the behaviour of the fish. Changes to their normal activities means it is time to get out the test kits. This is the best part of having the pond anyway so spend some quality time with your Koi and get to know them.