General Hardness (GH) is a measure of the dissolved mineral content in water, specifically the concentration of divalent cations, primarily calcium ($\text{Ca}^{2+}$) and magnesium ($\text{Mg}^{2+}$) ions. These minerals are naturally present in water sources and are reported in units of parts per million (ppm) or degrees of General Hardness (dGH). The stability and suitability of these water parameters are crucial for the health and well-being of aquarium fish. This article examines the specific level of 180 ppm GH, which translates to approximately 10 dGH, to determine its impact on various fish species.
Understanding General Hardness (GH)
General Hardness quantifies the total amount of calcium and magnesium dissolved in the water column. These two minerals are absorbed by fish, mainly through the gills, where they play a role in numerous biological functions. Calcium is important for bone structure, enzyme function, and the development of eggs, while magnesium is involved in metabolic processes.
GH must be distinguished from Carbonate Hardness (KH), which measures the concentration of carbonates and bicarbonates. While GH relates to the overall mineral content, KH is a measure of the water’s buffering capacity, which helps stabilize the pH level. Both parameters are measures of water hardness and must be monitored for a stable aquatic environment.
Is 180 GH Bad? Species Tolerance
A GH reading of 180 ppm (approximately 10 dGH) is classified as moderately hard water, and its suitability depends entirely on the specific fish species being kept. This level is not inherently harmful, but it falls outside the preferred range for certain specialized fish.
Soft Water Species
For soft water species, such as Discus, Angelfish, and Neon Tetras, a GH of 180 ppm is too high and can cause chronic stress. These fish originate from environments like the Amazon basin, where the water is mineral-poor, often requiring a GH below 5 dGH. Maintaining them in water this hard forces their bodies to constantly regulate internal salt balance.
Moderately Hard Water Species
Conversely, 180 GH is acceptable or ideal for many common community fish and livebearers. Species like Guppies, Platies, and Swordtails naturally inhabit harder water and thrive in the moderately hard range of 8 to 12 dGH. For these fish, 180 ppm provides the necessary calcium and magnesium for healthy growth and reproduction.
Hard Water Species
Hard water species, most notably African Cichlids from the Rift Lakes (Malawi and Tanganyika), prefer even higher mineral concentrations. While 180 GH is tolerable, it may be on the lower end of their preferred range, which often extends above 12 dGH. Aquarists may choose to increase it further to replicate their native conditions fully.
Effects of Inappropriate GH Levels on Fish
When the GH level is significantly outside a fish’s natural tolerance range, it directly impacts the biological process of osmoregulation. Osmoregulation is the mechanism by which a fish maintains the correct balance of water and salts within its body relative to the external environment.
In water that is too soft (low GH), the fish struggles to absorb essential minerals like calcium and magnesium necessary for gill function. Conversely, in water that is too hard, such as 180 GH for a soft water species, the fish must expend excessive metabolic energy to excrete the constant influx of minerals. This continuous energy expenditure leads to chronic stress, which weakens the immune system and makes the fish susceptible to disease.
Inappropriate GH levels can also affect reproductive success, particularly in soft water species. High GH can cause the eggs of these fish to harden prematurely, preventing the sperm from penetrating the egg membrane and resulting in failed breeding attempts. Furthermore, the presence of calcium ions in the water has a protective effect, helping to block the uptake of toxic substances like nitrite through the gills.
Adjusting and Maintaining GH Levels
If a GH of 180 ppm is found to be unsuitable for the chosen fish species, there are specific methods to adjust the mineral content.
Lowering GH
For soft water fish, the most effective way to lower GH is by using Reverse Osmosis (RO) or Deionized (DI) water. These filtration systems remove nearly all dissolved solids, producing water with a GH near zero, which can then be mixed with tap water to achieve the precise, lower target level. Natural methods, such as filtering water through peat moss or adding driftwood, release organic acids and tannins that can slightly soften the water. However, these methods are generally less precise and slower than using RO/DI water.
Raising GH
To raise GH for hard water species, commercial GH boosters containing a balanced mix of calcium and magnesium salts are the most reliable option. Alternatively, materials like crushed coral, aragonite substrate, or limestone rocks can be added to the aquarium. These materials slowly dissolve, leaching calcium carbonate into the water, which increases both GH and KH. All adjustments to GH should be made gradually over several water changes to prevent shocking the fish. Consistent testing with a reliable water test kit is necessary to ensure the GH remains stable at the desired level.