Aquarium water parameters for a balanced fish tank

Below is an overview of vital aquarium water parameters. pH, nitrogen compounds, phosphate, silicate, chlorine, along with water hardness should be balanced for a healthy fish tank. Imbalances can trigger common problems such as algae outbreaks caused by high nitrates, and many other problems.

Water Hardness

General Hardness (GH)

GH primarily measures calcium and magnesium ions. It is important for breeders (some species require very soft water, which is hard to maintain, requiring constant monitoring for maximum success). Other then choosing the right fish for the existing conditions, the GH is not all that important for the average hobbyist.

Common measurements use ppm and the equivalent mg/l. The conversion of degrees into ppm and mg/l is by multiplication of 17.8 or vice versa.

Hardness defined:

defined as ppm degrees
soft 0 – 50 0 – 3
moderately soft 50 – 100 3 – 6
slightly hard 100 -200 6 – 12
moderatley hard 200 – 300 12- 18
hard 300 – 450 18 – 25
extremely hard 450+ 25+

Carbonate Hardness (KH)

KH measures dissolved bicarbonate and carbonate ions. They are commonly referred to as the buffering capacity. KH determines on how stable your pH will be and is therefore very important.

Picture this: carbonate ions bond with hydrogen ions (which is your pH). The more bonding the higher the pH. Lesser carbonate ions results in a drop of pH.

KH of 70 ppm and less, will initiate the pH crash.

Baking soda is known to increase KH and distilled water to decrease KH (as distilled water has a KH of 0).

We do not encourage attempting adjustments of these values unless it is absolutely necessary. Should you feel the need to make adjustments, please be cautious and take it slow. Be sure to carefully monitor any changes in KH and pH. If your fish and tank are thriving, it is not recommended any adjustments be attempted.


pH is the meaurement of hydrogen ions. Increased hydrogen ions (less bonding) result in a drop of the pH (more acidic water), while a decrease results in a pH rise.

pH = power of hydrogen.

pH is measured on a scale from 0-14. The neutral value is 7, while values below are more acidic (towards a car battery) and values above 7 more basic (towards dish soap).

Changes in pH are a common cause of fish fatalities. Fish can adapt to most pH levels, if not broadly out of range, but they can’t adapt to bouncing values.

This is because pH has a logarithmic function (mathematical – meaning ten-fold). In other words, a change in pH from 7 to 6 means 10 times more acidic water. A further drop to a pH of 5 equals 100 times more acidic water.

If you have to adjust the pH in your tank, always consider the carbonate hardness. The pH in harder water more difficult to adjust because it bounces back, while softer water is more easily adjusted. Keep in mind to change it slowly as it causes a lot of stress to your fish. Maintaining a stable pH is generally more the way to go.

Some other facts about pH:

  • Ammonia increases in toxicity with rising pH
  • Nitrifying bacteria experience a growth and action reduction starting at a pH value of 6 and lower

Nitrogen Compounds

Ammonia build-up results from a break-down of fish metabolism. As ammonia (NH3) constantly converts to ammonium (NH4+) and vice versa, ammonia test kits usually measure both, resulting in a total ammonia (ammonia-N) concentration.

In an established tank, the reading of this test must show an undetectable level at all times. A detectable presence of total ammonia requires immediate action.

Ammonia is highly toxic in freshwater tanks, but even more toxic in reef and saltwater environments. This is due to a higher pH level that causes the presence of ammonia gas, which in turn is far more toxic and easily water soluble.

Even low concentrations of ammonia-N severely stress fish, making them vulnerable to diseases therefore shorting their life span. Accumulating ammonia will not only be highly toxic and cause severe stress for the fish, it will be lethal!

Nitrite represents the second stage in the nitrogen cycle. As nitrifying bacteria are readily available they will build a colony as soon as the nutrient source (ammonia) is available.

While ammonia is being converted predominantly by the species of nitrosomonas, nitrobacter is mainly responsible for converting nitrite into nitrate. When setting up a new tank, the nitrogenous compounds will rise to high levels. This enables the bacteria to form a colony and to start the conversion process (nitrogen cycle).

Nitrosomonas and Nitrobacter are aerobic bacteria and need a constant flow of oxygen in order to survive and to perform their tasks.

Nitrite levels should be at an undetectable level at all times after the tank has fully cycled. Not as dangerous as ammonia, but still a highly toxic chemical, Nitrite causes stress for fish even as low as 0.5 ppm. Levels exceeding 10-20 ppm are lethal over a period of time. Immediate action is required if high nitrite levels persist after 7-10 days.

Nitrite interferes with the oxygen metabolism, it destroys the hemoglobin (oxygen carrying cells) of the fish, and aquatic livestock.

Nitrate is the result of the bacterial breakdown of ammonia > nitrite > nitrate which is the final stage of the natural biological metabolic waste conversion also known as the nitrogen cycle.

Although less toxic than ammonia/ammonium and nitrite, nitrate as a nitrogen compound also causes stress at all levels making a fish’s organs work harder to adjust to it’s new environment. The increasing stress results in the loss of ability to fight diseases, the ability to heal itself, and the ability to reproduce.


Phosphate as a by-product of mineralization of dead matter such as plants, bacteria, feces, uneaten food, fish slime etc. are all internal contributors.

Dead plant material or rotting food particles settle either on the substrate or within the filter. Rinsing filter materials and vacuuming the aquarium gravel at every water change can significantly reduce potential phosphate accumulation from these internal sources.


The most common points of entry are the substrate, salt, and water. Please keep in mind, that R/O and D.I. units (filters to purify tap water by membranes or by chemical/ mechanical processes creating distilled water) will prevent silicates only for a few days, before they find the way through the membranes.

Another form of silicates is silicid acid, created by decaying organic matter. Same as phosphates, they can be water insoluble at a high pH, and become readily available with decreasing pH levels.

Chlorine / Chloramine

Water companies add chlorine or chloramine as a disinfectant to tap water. Chlorine is less stable then chloramine and airs out in just a few days. Some hobbyists simply let the water age for a couple of days before doing the water change, thus airing out the chlorine.

Chloramine is much more stable. That is why communities switch from chlorine. As it is very stable, it does not air out even if heavily aerated.

Chloramine, a mixture of ammonia and chlorine, passes (unlike chlorine) through the fish’s tissue directly into the bloodstream. In the blood, just like nitrite, it destroys the oxygen carrying cells. Chloramine can cause all fish to die within 24 hours.


Carbonate hardness, pH, nitrate, and ammonia/nitrite (salinity for marine tanks), should be tested on a weekly basis. Also be sure to test the water used during water changes.

The water parameters and definitions in this issue are intended to help you understand the conditions in your aquarium. A healthy aquarium requires immediate attention should one of these parameters produce dangers readings.

Other parameters such as trace elements i.e. iron, copper, calcium etc. should be checked on, if you add them in some way (as supplement or fertilizer).

Depending on the set up (marine/reef/plants), other factors come in to play, such as dissolved oxygen, redox potential or CO2.

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What is the acceptable level of phosphate in aquarium freshwater?


Use RO/DI (Reverse Osmosis/Deionized) water from an LFS (Local Fish Store) or even Distilled Water, those have lower pH. Nitrates can be cleared up with water changes. You can also install an RODI filter in your house so it’s always on-tap.


Simplified, hard water (high dissolved mineral content) has a higher pH compared to soft water (low dissolved mineral content). In order to lower the pH, the water needs to be softened by lowering the dissolved mineral content. This can be achieved by using peat moss, or using demineralized water for water changes, such as R/O water or distilled water.
Nitrates can effectively be removed using Algone. Causes for high nitrates can be overfeeding, overstocking, and a relaxed maintenance schedule.

Deborah York

my ph & nitrates are always high & my water is hard or very hard what can I do to fix these?