Altering Your Water's Chemistry
Water Chemistry
Water in nature contains dissolved salts, buffers, nutrients, etc., with exact concentrations dependent on local conditions. Fish (and plants) have evolved over millions of years to the specific water conditions in their native habitats and may be unable to survive in significantly different environments.
Fishkeepers need to know enough about water chemistry to ensure that the water in their tank has the right properties for the fish that they are keeping.
Water has measurable properties that are commonly used to characterize its chemistry. They are pH, kH (alkalinity), GH (general hardness) and salinity. In addition, there are several nutrients and trace elements.
PH (acidity/alkalinity)
pH refers to water being either acid, alkaline, or neither
(neutral). A pH of 7 is said to be neutral, a pH below 7 is acidic
and a pH above 7 (neutral) is alkaline. The pH scale is logarithmic. A pH of 5.5
is 10 times more acidic than water at a pH of 6.5. Thus, changing the
pH by a small amount (suddenly) is more of a chemical change (and more
stressful to fish!) than might first appear.
To a fishkeeper, two aspects of pH are important. First, rapid changes in pH are stressful to fish and should be avoided. Changing the pH by more than .3 units per day is known to stress fish. Thus, you want the pH of your tank to remain relatively constant and stable. Secondly, fish have adapted to thrive in a (sometimes narrow) pH range. You want to be sure that your tank's pH matches the specific requirements of the fish you are keeping.
Most fish can adjust to a pH somewhat outside of their optimal range. If your water's pH is naturally within the range of 6.5 to 7.5, you will be able to keep most species of fish without any problems. If your pH lies within this range, there is probably no need to adjust it upward or downward, although doing so (to the specific requirements of an individual species) will result in optimal condition of the fish in relation to colouration, breeding etc..
KH, (buffering capacity)
Buffering capacity refers to water's ability to keep the pH stable as acids or bases are added. pH and buffering capacity are intertwined with one another; although one might think that adding equal volumes of an acid and neutral water would result in a pH halfway in between, this rarely happens in practice. If the water has sufficient buffering capacity, the buffering capacity can absorb and neutralize the added acid (fish/plant wastes) without significantly changing the pH.Buffering has both positive and negative consequences. On the plus
side, the nitrogen cycle produces nitric acid (nitrate). Without
buffering, your tank's pH would drop over time. With
sufficient buffering, the pH stays stable. On the
negative side, hard tap water often almost always has a large
buffering capacity. If the pH of the water is too high for your fish,
the buffering capacity makes it difficult to lower the pH to a more
appropriate value.
In freshwater aquariums, most of water's buffering capacity is due to carbonates and bicarbonates. The term alkalinity should not be confused with the term alkaline. Alkalinity refers to buffering, while alkaline refers to a solution that has a pH above 7
Most aquarium buffering
capacity test kits actually measure KH. The larger the KH, the more
resistant to pH changes your water will be. A tank's KH should be high
enough to prevent large pH swings in the tank over time. If your KH
is below roughly 4.5 dH, you should pay special attention to your
tank's pH ie test weekly until you get a feel for how stable the
pH is. This is important if you neglect to do frequent
partial water changes. In particular, the nitrogen cycle creates
a tendency for an established tank's pH to decrease over time. The
exact amount of pH change depends on the quantity and rate of nitrates
produced, as well as the KH.
General Hardness (GH)
General hardness (GH) refers to the dissolved concentration of magnesium and calcium ions. When fish are said to prefer soft' or hard water, it is GH (not KH) that is being referred to.Although the three properties GH, KH and PH are distinct, they all
interact with each other to varying degrees, making it difficult to
adjust one without impacting the other eg Increasing the KH of the water also usually increases pH as well.
Water hardness is measure either in dH (degrees hardness) or PPM (parts per million)
General Hardness
0 - 4 dH, 0 - 70 ppm : very soft
4 - 8 dH, 70 - 140 ppm : soft
8 - 12 dH, 140 - 210 ppm : medium hard
12 - 18 dH, 210 - 320 ppm : fairly hard
18 - 30 dH, 320 - 530 ppm : hard
Salinity
Salinity refers to the total amount of dissolved substances. Salinity measurements count both GH and KH components as well as such other substances as sodium. Knowing water's salinity becomes important in salt water aquariums but in freshwater tanks, knowing pH, GH and KH usually suffices, unless keeping fish from estuarine areas.One component of salinity that neither GH or KH includes is sodium. Some freshwater fish tolerate (or even prefer) a small amount of salt (it stimulates slime coat growth). Moreover, parasites (e.g., ick) do not tolerate salt at all. Thus, salt in concentrations of (up to) 1 tablespoon per 5 gallons can actually help prevent and cure ick and other parasitic infections.
On the other hand, some species of fish do not tolerate ANY salt well. Scaleless fish (in general) and some Corydoras catfish are far more sensitive to salt than most freshwater fish. Add salt only if you are certain that all of your tank's inhabitants prefer it or can at least tolerate it.
Nutrients and Trace Elements
In addition to GH, KH, pH and salinity, there are a few other substances you may want to know about. Most tap water contains an assortment of nutrients and trace elements in very low concentrations. The presence (or absence) of trace elements can be important in some situations, specifically:- nitrates
- phosphates, the second most prominent nutrient. Phosphates have been linked to algae growth. If you have persistent algae problems, high phosphates may be a contributing factor. In a planted tank, ideal phosphate levels are .2 mg/L or lower. To control algae, frequent partial water changes are often recommended to reduce nutrient levels. If your tap water contains excess phosphate, water changes may be aggravating the situation. Your local water company can tell you what the exact phosphate levels are.
- iron, manganese and other trace elements. Plants need iron in trace quantities to grow. Tap water in many areas contains no iron at all.
