How to do Proper Water Changes/Additions

More fish are killed or hurt with improperly done water changes than any other reason, next to poor water quality and not testing the water in the pond. 

Most people do not realize just how complex water actually is, or understand all of the chemical and biological activities that are associated with it when it comes to housing fish. These chemical and biological processes are constantly trying to change the waters basic makeup, and it is important that you control these changes, and keep it as healthy and STABLE as possible for fish. Water changes and additions that are done incorrectly can harm or even kill your fish! This is especially true when your source/new water is tap/city water that has chlorine or chloramines in it!

Understand that a fish’s body is basically comprised of fluid, (just as human bodies are), and most of that fluid is in the form of water. That given, this makes fish bags of water, separated by a thin membrane, (their skin and scales) living in a water environment. Basically put, they are the water; therefore, any change that occurs in the water will instantly affect the fish. In nature, these changes occur slowly, but in the small, recirculating environments of our ponds or tanks they may occur too quickly and harm the fish. Fish require stability in the water to stay healthy, especially when it comes to parameters such as temperature, pH, and many other things as well. This is discussed in detail in the other articles such as The Science of Water.

Not only are water changes required during and after certain treatments, they should also be done for general health and maintenance of your pond or tank. Let’s just say that water gets “used up” after a given period of time, and will have to be freshened with the addition of new water.

I cringe every time I see the blanket statements that you should change your water or a percentage of it every week or month or whatever!

You will hear many varied opinions as to how often routine water changes are required, but the frequency and percentage of change totally depend on all of the variables associated with YOUR pond , tank, or the treatment protocols listed above, as well as the condition of your source water, be it well or tap water. In my opinion, when it comes to routine water changes, no one can tell you how often you will need to do them. What does determine the amount and frequency of water changes should totally be dictated by testing your water for pH, kH, ammonia, nitrite, and nitrate to name the most critical, as well as the treatment protocols listed above.

I can tell you right now that folks that have chlorinated source water may not want to do as frequent water changes as some that have well water. This is because water changes and additions with chlorinated water MUST be done in a very specific way!

Other variables such as dissolved organic compounds (foamy water), algae blooms, mineral content, and fish load will also play a role.

Now, understanding how a change in water chemistry can affect the fish, it is vital to know the parameters of the new source water, as compared to the ( existing or existing to remain), pond or tank water. The number one parameter to be concerned with first is the temperature, followed a close second by pH. As mentioned above, you need to compare the parameters of the new water to the existing to remain water, or the water that is to be removed. The more different they are in temperature and pH, the slower the change needs to be done.

Normally, if there is a difference in temperature of more than 5 degrees between the new and existing water, and you are doing more than a 20% change, you need to be careful, especially if the new water is colder than the existing water. This is especially true when it comes to fish that are less than 6 inches or so. These little ones you need the temps to be within a degree to keep them safe!(Anything less than a 20% water change will usually not be a serious consideration, and will not affect the fish if there are slight differences.)

If you add water that is colder too quickly, you are in danger of cold-shocking the fish, and this is especially true the smaller the fish. Remember stability? In nature, the mid to lower depth water temperature does not change quickly, only the surface temperature does, and the fish can easily escape the change on the surface by retreating to the deeper depths. In most cases, our shallow ornamental ponds don’t afford them this option, as the temperature is fairly consistent from surface to bottom. Therefore, if you are forced to add colder water to the tank or pond, do it as slowly as possible, as not to change the existing temperature in the pond or tank more than one degree an hour. The larger the difference though, the slower you will want to do it. In other words, if you are adding water that is 50 degrees to a pond or tank that is 75 degrees, you may only want to see a change of one degree every two hours. The slower the change the better with as large a difference in temperatures as this.

The pH is also a critical parameter to consider when doing a water change. The pH scale is logarithmic, and for every change in pH of one point, the pH has changed tenfold. For example, a pH of 8 is one hundred times more alkaline than a pH of 7, so as you can see, even a minor difference in readings is a substantial chemical change. Another consideration is whether your existing water contains any ammonia, as this compound becomes increasingly more toxic as the pH rises above 7. In other words, the higher the pH is above 7, the more poisonous any ammonia in the water becomes. So in the case you are doing a water change to dilute out any ammonia, make sure you realize the pH of the new water, and if it is above 7, you should also add some type of ammonia binder or detoxifier as well.

Water Changes with Chlorinated Water Sources


If your source water is “city” water that contains chlorine or chloramines it is critical to be VERY careful doing water exchanges. If done incorrectly, these types of water changes or additions that have ANY form or ANY concentration of chlorine or chloramines will hurt or even kill your fish and your biological filter! At minimum if done incorrectly and the fish live thru it, their lives will be shortened substantially if the water addition or change is not done correctly!

As most of you may know, local municipalities add various chemicals to the water to make it safe for human consumption. The two most common chemicals used are chlorine and chloramines, and both are deadly in ANY concentration to fish! It is for this reason that this type of source water must be treated with a dechlorinator properly, and made safe for fish. This dechlorination MUST be done BEFORE the fish come into any contact with these deadly chemicals! Remember these chemicals even at the lowest concentrations are deadly to the fish!

To understand how to do water changes and additions safely, you must understand the whole nature of how, when and why municipalities make water safe for humans with the additions of chemicals such as chlorine and chloramines.

All over the USA domestic water is obtained from various sources. Reservoirs, wells, storage tanks etc. This water is commonly treated with chemicals as discussed when speaking of city or tap water. This treatment is done to kill any harmful bacteria and such that can make people ill. This can also be the case in some housing developments or small towns that use a common well to supply the water to the local residents. The housing developments, small towns , and even places like fairgrounds and other public type places sometimes have their own smaller treatment facilities that they themselves control and maintain on a local basis. In other words the state government is not involved in the treatment or monitoring of these type treatment facilities. These place sill however are supposed to be using state and federal guidelines for treating these waters to make them safe for people. However, as you can imagine, without strict regulations by larger government, these small places can and do under and overdose these chemicals occasionally.

According to EPA guidelines, they want to see at least .3(point three) ppm(parts per million) chlorine to each end user of that water. This is considered the lowest level of chlorine that will do the job killing any harmful bacteria or contaminants in the water supply. As well they do not want more than 3 to 4 ppm total chlorine going to any household as this amount can make people sick as well.

Now knowing these facts, understand that chlorine dissipates due to certain variables like , contaminant levels, as well as the distance it is being pumped. As the water moves down the line to each household some chlorine is lost. So this means that the water coming from the treatments plant cannot have a greater concentration of chlorine than the 3-4 PPM and still must maintain the minimum level of ‘3 (point three) ppm by the time it gets to the last user in line and farthest from the treatment plant.

What this means is that depending on these variables of distance, contaminants and other factors the water directly out of the treatment plant may have higher levels to start with. I have seen levels up to 10ppm in some places right out of the plants. This is dangerously high, but based on those variables by the time it get to the first house in line from the treatments facility contaminants and such have caused most of that 10ppm to be used up or dissipated. Remember, the goal to get the minimum ;level of disinfectant to each and every household yet keeping anyone from getting an overdose above 3PPM total. Understand as well that chlorine levels can be adjusted and raised and lowered based on other seasonal factors, as well as flooding and such in the reservoirs. Below is a diagram to illustrate the process;

So what does all this mean to you? In short it means you need to test your chlorine level of your source water each time you do any major water changes or additions. Remember that your levels can change as discussed, so to properly dechlorinate your water to make it safe for fish, you must know what level of chlorine you are treating. This means you need a PROPER chlorine test kit that is dependable and accurate. We have these in our online store here;

Chlorine & Other Test Kits

How to Properly Dechlorinate Water

As discussed ANY amount of chlorine or chloramines is harmful to fish! This water must be properly treated and dechlorinated BEFORE it ever comes in contact with your fish or filter. It also means you need a chlorine test kit and test the chlorine level at the time of the water change or addition. Once you know the ppm of total chlorine you can then determine how large a dose of the dechlorinator to be used.

Once you have determined the chlorine level add the proper dose of dechlorinator to be used per gallon it is easiest to have a tub, barrel or other holding system with a KNOWN gallonage or volume. Things like a 55 gallon drum, kiddy pool or whatever you know the true gallons it holds. Then you fill that container with the new chlorinated water.  Now you add the appropriate dose of dechlorinator and mix thoroughly. Once mixed, you can dump or pump that water in the pond or tank that holds the fish. In this manner the new water has been properly dechlorinated and will be safe for the fish and you filter. This is the ONLY way to be sure the water is safe for the fish and properly dechlorinated

DO NOT attempt to drain water from the pond, then make a guess on how many gallons you removed that will be replaced and try to add dechlorinator and then filling system again. Firstly it is a huge guess as to how many gallons you took out and thus added back, and secondly the water will not get fully dechlorinated or fast enough to be safe for fish.

Well water Changes and Additions

In addition to the precautions discussed in the beginning of this article, it is also a good idea even when you have well water to use a cheap water meter you can buy at your local home improvement store. These meters have selectable time frames you can choose for the hose run time. They hook directly to any standard hose connection and can be set to run as long as you choose and then automatically shut off. With these installed there is little chance of forgetting turning off the hose and killing you fish with temp shock or large pH changes.

Also I do not recommend any auto -fill valves on any ponds. Whether you have well water or city water. If you already have one disable it! Many pond installers put these in and they are simply too dangerous as they fail and also not feasible for city water.

Written by John Fornaro, Hanover Koi Farms. ALL RIGHTS RESERVED BY HANOVER KOI FARMS, COPYRIGHT © 2018

Back to Top
Previous Page