As our hobby progresses, more and more people know the importance of testing their water quality. Nitrogenous wastes are the ‘big three’ and have a huge impact on the welfare of our aquatic pets – especially in newly set up aquaria.
To recap, Ammonia (excreted directly by aquatic life) is very toxic, as is Nitrite (the first stage in decomposition) and the residual Nitrate (the least toxic stage) can be harmful and will accumulate in systems that lack a biomass of plants, algae or other means to remove it. Nitrate is a large part of the reason why partial water changes are essential for most aquaria.



There’s more to our water parameters than nitrogen-based compounds though and some of these are more significant than others. For freshwater keepers it’s true to say that there’s a whole host of popular domesticated species that are hugely adaptable but for some other fish, inappropriate water chemistry can lead to problems. The rise of online groups has blurred the boundaries of this somewhat, leading to some zealotry and creating problems where none exist. For decades, many successful hobbyists have been happily mixing species whose ancestors swam in very different water parameters and their pets have thrived. This approach is still the best for most hobbyists, who can be guided by their local store – many branches run soft or harder systems for those species that have special requirements. As your hobby progresses, you can decide to specialise or perhaps select fishes that are most at home in your local tap water.

Before looking closely at some of the values you might want to adjust, it’s pertinent to say that stability and quality are important factors to bear in mind. Many of us have seen aquarists chase ideals, such as low pH, only to become reluctant to perform water changes for fear of altering their hard-won value. If you choose to manipulate the water chemistry in your aquarium, don’t forget to make provision to adjust new water to match as part of your regular maintenance regime. There’s no point providing a pH of 5.5 for your delicate blackwater species if you then allow nitrates, phosphates and background organics to rise to a point where they become problematic. In these circumstances, new water needs to be processed and the necessary buffers or conditioners added before use in order to facilitate essential regular water changes.

Carbonate hardness or KH is one of the biggest factors for some key groups of fish. If you’re interested in keeping pedigree guppies or fancy goldfish, you’ll find they’ll often be challenging in soft water and respond well to values of 10dKH and higher. It’s something of a generalisation but most aquarium livebearers do better in hard water, although some wild populations come from water that would be better suited to keeping Discus. As even softwater fish need biologically available calcium to function, it’s important to check KH even for low pH systems. Not only can pH crash in water with no mineral content, but fish can too – often leading to asymptomatic losses as outwardly healthy animals suffer organ failure. Blackwater fishes have evolved to cope with very low levels of minerals and diet becomes a more crucial source of trace elements etc in these circumstances. Only very healthy fish with negligible stressors should be kept in these conditions, although exceptions can be made for short-term keeping, such as spawning tetras etc.



Phosphate is another significant parameter to monitor as it fuels nuisance algae growth in all types of aquaria and can be linked to ailments such as HLLE or Hole in the Head disease in freshwater fishes such as cichlids. It can also impact marine invertebrates whilst encouraging undesirable algal competition. Testing phosphate can often shed light on stubborn problems and levels can be high in tap water due to its use in safeguarding public health by preventing lead pipes dissolving. Agricultural run off is another factor which means phosphates can be high in both urban and rural areas. Look out for pH buffers based on phosphoric acid, as these tend to send levels through the roof. Other sources of phosphate are frozen foods, which are best rinsed of their juices before adding them to the aquarium.


When moving on to marine aquaria, there’s the old saying that you ‘shouldn’t add anything that you’re not testing for’ and that is sound advice. It may seem that a population of hard corals has a relentless appetite for calcium and magnesium but it’s good to know what the levels are and avoid an optimistic overdose that may do more harm than good. One of the biggest differences between running a tank of corals and a tropical tank is monitoring parameters such as alkalinity that changes frequently and is hard to estimate visually. Like a densely planted freshwater aquarium, photosynthetic corals will also have a need for low levels of nitrate and that might take a little tinkering too.
So, you can see that it builds into a picture where water testing and researching the preferences of the animals in your care is very much the key to successful aquarium keeping. Familiarity can lead to a quick assessment of system health by eye but many situations are significantly easier to remedy when you see the problems developing through vigilant testing.