|MadSci Network: Zoology|
Thanks for your question. I'm having problems finding info on it as well. To start I want to discuss Dissolved Oxygen (often called D.O. by those testing water). D.O. in water varies due to many reasons 1) The temperature of the water - you can force more oxygen into cold water 2) Biological activity using it up - fish and other animals breathing it in and converting it to carbon dioxide, decaying matter such as plants, dead animals etc, by micro-organisms using it up 3) Plant respiration - the oxygen / carbon dioxide role of plants 4) Time of day - photosynthesis of plants has 2 cycles; a day and a night cycle 5) The flow of water - water flowing over rocks and the like will have more opportunity to take on oxygen from the air 6) Surface area - similar to number 5 but the bigger the area the more space for oxygen to enter the water And I'm sure there are others. My point is that your fish tank is not a closed system so its is subject to all the above also. Oxygen will vary dependant on the number of fish, how much algae you allow to grow, whether you have plants, your pump, the surface area of the top of the tank v's the volume of water it holds (this is the reason that some people have a single fish in a big wine glass with no need for a pump), how often you change the water (usually just a part etc). I know this is not directly answering your question but it's all important. More on fish at www.petlibrary.com/goldfish/advcare.htm and water quality / testing at http://fs.huntingdon.edu/biology/HTI/water.html Now...when an animal hyperventilates (breathes to fast) its constricts some of its blood vessels which restricts some of the blood going to its brain. At this time the hemoglobin (part of blood requiring oxygen) becomes less efficient at releasing oxygen. So there is less blood reaching the brain and the blood gives up less oxygen. This obviously sends the signal to "breath more!" and the animal gets into a vicious cycle. Unfortunately this over breathing is pretty hard work so the animal then also needs more oxygen to sustain the exercise. The resultant panic continues the cycle and the breathing becomes more and more shallow (from chest not diaphram) which is very inefficient (though this is in air-breathers, not fish). http://maxpages.com/livingpanic/hyperventilation The problem is that dependant on who you read, some argue that the problem is less about the oxygen going in and more about the carbon dioxide going out. This can cause changes to blood pH (how acid or basic your blood is), nutrient deficiencies, muscle fatigue etc all of which affect how efficiently your blood can hold, transfer and requires oxygen. If you're interested read: http://www.breathing.com/articles/hyperventilation.htm I guess i am dodging your question to a certain extent but here goes... You are right that if you add calcium carbonate to the water than you will affect the fish's respiration. However this may be due to several reasons. equation: CO3 and 2H+ > CO2 and H2O CACO3 is very basic so it will affect the pH of the water which (as above) and affects how much oxygen the water will hold. Be careful though because fish have a optimum survival pH range (around 6.5 to 8.2). You may reduce the oxygen but hurt the fish due to the new pH - over 10.5 is lethal to carp and over 11 is rapid lethal to all fish http://fs.huntingd on.edu/biology/HTI/water.html. Putting CACO3 into water filled with the acidic fish waste would release carbon dioxide (equation CO3 and 2H+ > CO2 and H2O) therefore changing the CO2 / O2 balance. Anyway...getting closer to your answer. I could not find any literature on fish having adverse affects due to too much oxygen. There is a lot of too little - eg minimum for carp is about 2.0 mg/L - http://fs.hunting don.edu/biology/HTI/water.html). This is probably because the water would not physically likely hold "too much" due to all the environmental issues i raised above. Even if it did it would not stay in the water very long at reaonable temperatures and air pressure. Looking at the fish literature carp can happily live in water as low as 10 degrees celcius. In the coolest of "moutain streams" this would allow for a D.O. up to 15 mg/L. There is no way you could get that much oxygen in your room temperature tap water. So, your solution would change the O2 available in your water but it is most likely not necessary. Peter P.S. According to a chemistry professor that I know, fish may have problems breathing in tap water due to the disolved chlorine gas
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