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Water Quality in the Fish Pond

Keeping the water quality high in the fish pond is a very important aspect of keeping the fish healthy on a long term basis. They are dependant on you to make sure that everything is as pristine as possible, in their natural habitat ammonia, nitrites and nitrates are not a problem as they do not live in a closed environment such as a fish pond, in the fish pond the filter can deal with ammonia and nitrites by means of the filtration system but nitrates build up over time and can affect the fish. By means of cycling the fish pond filter we know that by adding the fish it can cope with their waste and any ammonia passed through their skin but we still have to monitor this as it is still possible for mini cycles etc. to occur especially if it is fairly recently that the fish pond was actually cycled.

Allowing the water quality to drop will lead to the immune system of the fish to weaken leaving them susceptible to disease and other problems, it only takes one fish to contract this disease before it spreads right through the fish pond leaving you with a batch of sick fish and one large problem trying to get things back in line.

The water parameters can be monitored by means of using testing kits ( these will be covered further into the article), getting into the habit of testing the water on a regular basis will give you a head start on any drops in the quality levels and more importantly give you time to react before it all gets out of hand.

There are several parameters that do need monitoring more than others so we will cover the main ones on this page to give the the best start for your fish pond. The most important point to cover before we go any further is to ensure that your fish pond is cycled before you add any fish, cycling with fish is possible but it will place unnecessary stress in them, much better to be patient and make sure that the filtration is up to scratch.

Ammonia in the water is highly toxic to the fish, if the filter is working efficiently then any test readings should always be at zero, if you start to get a positive result for ammonia you have either added too many fish to the pond or you have added them too quickly and the filter needs time to catch up with the stocking, i.e. the beneficial bacteria need time to expand their colonies inside the filter to deal with the extra fish waste. It could also be that you are overfeeding the fish and food is being left at the bottom of the fish pond decaying and releasing ammonia into the water column.

Ammonia is highly toxic the the fish and as the pH increases in the water, ammonia has a greater effect on the fish as does higher water temperatures. Tell tale signs of ammonia presence can be burns on their bodies or signs of restlessness and agitation by the fish as they become stressed.

The readings for nitrites should also be zero, signs of a positive result are more or less the same as with the ammonia but nitrites are less toxic but they can still do permanent damage to the fish and lead to mortalities over time.

In a perfect world we would also have zero readings for nitrates but it is very rare that this ever happens, mostly you would expect readings between 10-20, if you have plants in your fish pond they will feed on the nitrates , if the nitrates keep rising then it is time to perform partial water changes until the levels drop again. It has been stated that fish are fine with levels of up to 100 ppm, I have never allowed the nitrates to rise this high before reacting to the situation so always think in advance, at the first sign of a rise, remove a percentage of the fish pond water and replace with fresh, conditioned water.

This next section is often the one that can confuse many fish keepers of aquariums and fish ponds alike. You will also need to monitor the pH and the KH of the water. The two are relative to each other but if explained separately it should become clearer.

The pH of the water may fluctuate directly after the fish pond has cycled, it can take many weeks for this to become stable and once this happens your fish pond is classed as mature. With my fish pond I always aimed for a pH of 7.0, this is classed as neutral. Lower than this figure and the water becomes acidic, this is not good for most freshwater fish, if it rises above 7.0 then the water become alkaline. A figure slightly above 7.0 is not a serious problem, for example my mains water reads at 7.6 and this is still perfectly acceptable but once the water is added to the fish pond is does drop down to 7.0 after a couple of days. This also highlights why the partial water changes should not be too large, sudden changes in the water parameters can affect the fish so my limit was always 10% of the water volume with any given water change. If you do find that the pH drops below the neutral mark there are commercial products available that can stabilise the pH, the way to go is to adjust the pH with either pH up or pH down and then add the stabiliser to the fish pond water to lock it. This process should not have to be repeated too often of the fish pond is balanced but there are many factors that can affect the pH.

Over a 24 hour period the pH will change, this is a fact that cannot be prevented and is perfectly normal, when checking your pH always do the test at the same time of day each time. The amount of CO2 that the plants release into the water, dissolved compounds in the water are just two factors that can affect the pH, the secret is to get the pH range into a controllable level where you are in charge and not the fish pond.

One vital factor can affect the pH badly, this is the buffering power of the water, basically the buffering power is the concentration of carbonate ions in the water, the higher the concentration, the better the buffering. This is where the KH comes into play, KH is the carbonate hardness of the water, I mentioned earlier how this is indirectly linked with the pH, well if the KH is too low then the water cannot buffer itself and the pH will start to drop. A reading of below 4 for the KH will mean that the water is unstable and you could end up with a pH crash which will definitely affect the fish. All of this may seem very complicated but believe me after a while it becomes second nature. The KH can be increased in the fish pond by slowly adding sodium bicarbonate, once you reach a level of 10 then this will mean that the water has good buffering power and the pH should remain at a stable level.

Testing kits for the water are readily available from any aquatic supplier, they can be basically put into two main groups. There are liquid test kits and test strips which take results of several parameters with each test. The liquid test kits are designed to test each parameter separately so a kit will be needed for ammonia, nitrite and nitrates as well as pH and KH. There is a test kit also available to test the GH (general hardness) but I have always found that if the KH is fine then the GH does not need to be worried about too much.

I personally favour the liquid test kits as they are more accurate than the test strips, with each strip covering a broad range of tests they tend to be more vague but will still give a good insight as to what is happening in your fish pond.

Whichever test kit that you do decide to use always make sure that they are in date, they only have a shelf life of 12 months in most cases and always follow the instructions carefully. The liquid ammonia and nitrate tests involve adding two reagents to a small amount if the pond water whereas the nitrite, KH and pH only involve one liquid. If a test result appears to be way out of range always do another test to double check, sometimes you may have accidentally contaminated the testing water when adding it to the tube so make sure before you panic!

Testing the water does need to be part of the monthly maintenance routine, being for-warned of any fast approaching problems gives you that bit more time to deal with the situation and in many cases totally prevents any major problems from actually occurring.

Question left on Sat, December 17, 2011 7:42 pm by Shehu Yusuf Bazata

What are the specific factors that can affect pond water quality and why?

Answer by staff: One of the major factors that can affect the water quality in a fish pond has to be overstocking, this can result in the filters not being able to cope with the large amounts if fish waste that break down to release ammonia into the water. Adding the fish before the filters are cycled will have the same effect as the beneficial bacterial colonies are not large enough to convert the ammonia produced. Other factors can include poor fish pond maintenance, if the pond does not get cleaned properly or the bottom of the fish pond allowed to build up with detritus.

Partial water changes may need t be performed 2-3 times through the summer months to refresh the mineral content in the water and reduce the nitrates, adding pond plants should keep the nitrates in check as the plants feed on these but some fish ponds are basic with fish only.
Question left on Mon, July 9, 2012 14:32 pm by alfie petchey

Hi there, I have a fishpond with all types of fish from koi, goldfish and mirror carp. They are breeding like mad and the water is beginning to smell. In the filter I noticed there are insects as well as in the water. I don't know what they are, think they look like crayfish type shrimp and I've got small snails on the brushes also in the filter there are small type red worms. The water is pumped around through a hippo pump through a UV into the filter then flows out into the pond via waterfall. Please, can you tell me if this is OK or what I must do to cure the smell and cleanse the water?Thank you, alfie.

Answer by staff: Having insects and snails in the filter is quite common and nothing to worry about. The smell could be coming from the bottom of the pond so this may need cleaning to remove any detritus. After cleaning it will help if you do a partial water change as some detritus could be suspended in the water.