Tropical Fish Keeping - Aquarium fish care and resources

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pop 12-10-2012 11:00 AM

Popís opinion TDS
I found the article Total Solids (TSS and TDS) in the Freshwater Aquarium to be a good read and lend a new consideration when thinking about water chemistry and the relationship between ph and TDS / TSS and the manifestation of these relationships in the aquariums water column.

We all are knowledgeable of ph and the general meaning of the readings. PH changes when the water dissociates in the water column and produces hydrogen ion (H+) and hydroxide ion (OH-). When the hydrogen ions equal the hydroxide ions the water column is neutral. When the hydrogen ions are greater than hydroxide ions the water column is acidic and naturally when hydroxide ions exceed the hydrogen ions the water column is basic (alkaline). Revealing that ph indicates the hydrogen ion concentration in the water column.

Total Dissolved Solids are well defined in Total Solids (TSS and TDS) in the Freshwater Aquarium article but I would like to amend the definition to include ammonia, nitrite and nitrate as well as dissolved carbon dioxide and bring notice to carbonate hardness (kh). TDS & TSS is a measurement of drinking waterís clarity and is not considered a measurement of pollution

Degree of kH
okH is a measure of carbonate and bicarbonate concentrations and reflects the buffering capacity of the water column.

citation, anions
Citations are elements that are located on the left side of the periodic table that when they react they frequently become positive ions. Examples of citations are sodium and calcium ions.
Anions are elements located on the right side of the periodic table that react with metals and take on electrons to form negative ions. Examples of anions are chloride, sulfide, and nitrate ions

The Story
There seems to be an uncanny relationship between (ph) and TGS element (kh). When the carbonate ions are concentrated, TSD are also in higher concentration state and the ph is elevated as well and it is also stable. The reason for this stability is the existence of high concentrations of carbonate ions that buffer that the water column preventing changes in the ph.
Carbon dioxide, ph alkalinity and hard water have a profound effect on the level of stress, fish health, oxygen availability and the toxicity of ammonia. An example is ammonia toxicity increases with the rise of ph and decreases significantly when the ph crashes,

Carbon dioxide/ bicarbonate/ carbonate buffering system.
The ph of water is determined from the dissolved compounds collected on the trip to your aquaria. When added to the aquaria the ph is also influenced by factors of the aquaria environment such as respiration of flora and fauna as well as photosynthesis. Without a buffering system these natural processes would result in large swings in ph which would have a negative impact on fish and plants. This is where the carbon dioxide/ bicarbonate/ carbonate buffering system steps in to stabilize the ph by collecting excessive hydrogen ions and then releasing them as the level drops maintaining stable ph.

CO2 + H2O H2CO3 HCO- + H+ CO32- (solid) + 2H+
What this formula tells us carbon dioxide given off by fish and plants respiration dissolves in water to form carbonic acid (H2CO). If pH levels increase, that is the water becomes more alkaline (say from plant photosynthesis), then the carbonic acid dissociates to form bicarbonate and hydrogen ions (HCO3- + H+). Hydrogen ions are acidic-forming ions and will therefore counteract the alkalinity increase. If the pH continues to increase, the bicarbonate will dissociate to form solid carbonate and release yet more hydrogen ions (CO32- (solid) + 2H+), to counteract the increased alkalinity. If pH levels start to fall the process is reversed.
The buffering capacity of water depends on the total amount of bicarbonate and carbonate present. Water that has low levels of these ions will quickly exhaust its ability to counteract pH fluctuations and crash.

TDS element calciumís role in biological processes can not be stress enough. Calcium is necessary for bone formation, blood clotting and other metabolic reactions. Itís the water and food that provides the needed calcium. The availability of free ionic calcium in the aquaria water column at relative high concentrations reduces the loss of other important salts as sodium and potassium from fishís body fluids as blood. It is critical the exact concentration of sodium and potassium is present for the normal heart, nerve and muscle function. Water that is low in calcium fish will lose substantial amounts of these necessary salts through osmoregulation.

Fresh water fish are saltier than the aqua environment they live in and osmoregulation is the process that allows fish to maintain the necessary fluid electrolyte (salt) for survival.
Osmosis is the tendency of water to travel through a semi-permeable membrane from areas of high electrolyte (salt) concentration to areas of low electrolyte (salt).
Because freshwater fishís body fluids contain several electrolytes (salts) the fish faces the potential of losing these necessary salts through osmosis. Fishís gills are a good example of permeable membrane; water from the environment goes through the gills to the inside of the fish and does so in large quantities. If this process were uncontrolled the fish would lose the necessary salts and suffer intolerable electrolyte loss through water waste elimination.
Freshwater fish address this problem in two general ways; in oxygen rich water column the fish reduces their respiration because they need less oxygen therefore reduces the amount of water influx through the gills. This solution will not work is oxygen poor water. Freshwater fish have chloride cells that are based around the gill filaments. that transports sodium, chloride and potassium ions from the water outside their body to the blood inside the body. This replaces the lost electrolytes through the large amount of urine. This process is the basis for the mis-guided view of adding salt to freshwater aquariums.


General Chemistry Online: FAQ: Acids and bases: What is pH?
pH Calculations - Chemistry Quick Review of pH
Hobbyist's Corner
Water Hardness and Fish Health

Interactions of pH, Carbon Dioxide, Alkalinity and Hardness in Fish Ponds
William A. Wurts and Robert M. Durborow

William A. Wurts, State Specialist for Aquaculture
Kentucky State University Cooperative Extension Program
P.O. Box 469, Princeton, KY 42445

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