Why Test Your Aquarium's Water

Testing your aquarium’s water conditions is a great way to ensure that you’re providing optimum conditions for your livestock, and that your equipment and maintenance routines are appropriate.

As you can see from the test kit section of our website, we stock a huge variety of aquarium test kits which are produced by numerous manufacturers to monitor more than 20 different water parameters.

We’re going to use this article to outline each of the parameters you can test for, explaining the importance of monitoring each.

Fundamentally, our livestock’s health depends upon the water conditions within which it lives – testing our aquarium water informs us of any potential problems which may be developing, prior to the loss of any livestock, as often such issues are invisible. We can also ensure we’re providing the correct levels of acidity, water hardness, etc., ensuring that our livestock thrives.


As organic matter breaks down within our fish tank, whether that be uneaten food, fish waste or the natural break down of any other detritus that can be found within the fish tank, ammonia is produced.

Ammonia is toxic to our livestock and elevated levels of ammonia will inevitably lead to losses.

The level of ammonia within an aquarium should be as close to zero as possible – especially in an established aquarium.

Ammonia is broken down by beneficial bacteria within your filter. When setting up a new tank, these bacteria will not have had time to become established. It is at this point that Ammonia levels will increase – and it is imperative that you don’t add livestock at this point or you will endanger them. When monitoring the Ammonia level over several weeks, you’ll notice that it subsides down to zero, as the bacteria become established. It’s at this point you’ll notice that the Nitrite level within the fish tank will start to increase. When the Ammonia level is down to zero, you’re nearly there – you just need to wait for the Nitrite levels to subside.

Monitoring Ammonia levels in the long term will indicate if your filtration system is performing correctly, or if you have over stocked your fish tank. As such, it’s sensible to keep an eye on Ammonia levels regularly, because if they increase, you know to take action.

We stock over 17 different Ammonia test kits, with products by Nutrafin and API recommended for newcomers, and products such as the Salifert or Seachem MultiTest being ideal for seasoned fish keepers. All provide accurate results and are easy to use.


Nitrite is also associated with the maturation process of a fish tank, as the beneficial bacterial that consume the Ammonia produced, create Nitrite as a by product. Nitrite is also toxic (if slightly less than Ammonia, it’s still problematic) – so it’s sensible to keep an eye on this too. A second strain of beneficial bacteria will develop over time within your filtration system, which breaks down the Nitrite.

When maturing your fish tank, you’ll spot that the Ammonia level will spike, at which point the Nitrite level will start to increase. This demonstrates that the cycling process is underway, with beneficial bacteria consuming the Ammonia and producing Nitrite.

As the second batch of beneficial bacteria become established, you’ll see the Nitrite level subside. When this is down to zero, it’s time to purchase (a small quantity) of livestock – and to make sure the Ammonia and Nitrite levels don’t increase again!

If you add too many fish at this point, you’ll run into problems, so patience is very much a virtue!

Again, it is sensible to monitor Nitrite levels, but you don’t need to do this as regularly as Ammonia or Nitrate.

We stock nearly 20 different Nitrite Test kits, with products for beginners and experts alike and that suit all budgets.


Nitrate is the final part of the nitrogen cycle that is associated with our aquarium’s filtration system. The beneficial bacteria that break down Nitrite produce Nitrate as a by product which is less toxic than Nitrite, but it can still cause lots of problems!

Nitrate builds up slowly over time and it’s all too easy to not realise what’s happening. Although there are specialist medias and filter systems that target the consumption of Nitrate, the great majority of fish keepers do not have these – and if you don’t do regular water changes, sooner or later you’ll have elevated Nitrate levels. Furthermore, Nitrate is totally undetectable without a test kit, so all too often you’ll be blissfully unaware until you start to lose livestock.

If you don’t test for any other water parameter, please make sure you test for Nitrate! If you see levels sneaking up, you can increase the number and size of the water changes that you do, or add a nitrate removing resin to your filter – potential problem solved!

With over 20 Nitrate test kits available, again we stock products suitable for both novices and experts.


pH refers to a level of acidity or alkalinity with a scale of 0 to 14 (and 7 being referred to as a pH of neutral). The lower the pH level from 7 the more acidic, alternatively the higher away from 7, the more alkali.

So why is it important to know the pH of our aquarium's water? The fish we stock in our tanks are native to regions throughout the world - and the water conditions, particularly the pH can vary. If we take the Amazon for example, where the majority of Tetra's such as Cardinals and Rummy Noses, freshwater Angel Fish and Discus are naturally found, there is a tremendous amount of precipitation falling on to the rain forests in the catchment area. Water quickly enters the rivers and streams, washing over rotting vegetation and without the time to soak into bedrocks. As such, the waters of the Amazon are Acidic. Alternatively, if we take the East African lakes of Tanganyika and Malawi, there is limited rain fall and vegetation, with water running permeating through limestone bedrock as it makes it's way to the lakes. As it does this, the water becomes more Alkali. The pH of water throughout the UK varies tremendously too, with water in the East Midlands being hard and alkali (some would say liquid concrete!), whilst water in the South West is usually acidic and soft.

It is important to match the water that you have available to the species that you keep whenever possible. Step one therefore is to checkout the pH of your tap water. If you want to keep fish with the minimum fuss, keeping species that naturally come from a region with a similar pH is a great way to do it, as if not you may have to adjust the pH of your water prior to adding it to your aquarium. This can be done using pH buffers or a Reverse Osmosis unit.

Whilst it is true that the majority of the (freshwater) fish available to the hobby are bred captively and have become accustomed to different water conditions, to get the best out of your fish, and if you wanto to successfully breed them, you'll need to keep an eye on pH and match the natural environment of the fish.

An interesting point to note is that pH can have a rather strange side effect when breeding fish. If we take the Cichlid species Kribensis (Pelvicachromis pulcher.) for example, if the pH is above 7.0, most of the offspring will be male, where as if it is below pH7.0, most will be female!

Whilt the pH of your tap water is not likely to fluctuate, it is possible for changes to result to an aquarium's pH due to substrates that are not inert influeing the pH. For example if Peat is used in the aquarium, the pH will lower, where as if gravel us used that is not lime free, the pH will increase.

As such, it's important to monitor pH to ensure you're providing the correct conditions for your fish in the long term.

We have a large range of pH test kits available from manufactures including Nutrafin, Tetra and Waterlife.

General and Carbonate Hardness

General and Carbonate Hardness tends to run in parallel with pH with soft water (low in General and Carbonate Hardness) being associated with acidic waters, whilst hard water (high in General and Carbonate Hardness) being associated with alkali waters.

General Hardness is a measure of the concentration of divalent metal ions such as calcium and magnesium (Ca2+, Mg2+) per volume of water. I won't go into details about what this means (as I haven't a degree in Chemistry!), other than to say that fish from the Amazon appreciate a low general hardness, unlilke Eastern African Cichlids.

Carbonate Hardness (or Carbonate Alkalinity) is a measure of the alkalinity of water caused by the presence of carbonate (CO32-) and bicarbonate (HCO3-) anions. It is usually expressed either as parts per million (ppm or mg/L), or in degrees KH.

Both of these hardness types have influence on the stability and pH of your aquarium's water, by providing a buffering capacity. The lower the hardness level, the easier it is for pH levels to change - which is not a good thing, particularly if keeping marine fish and inverts.

We have a large number of General and Carbonate Hardness test kits available.