Taken from FishYou.com (it's not a board so I don't think it could be considered as MFK ... mods, please feel free to disagree)
The whole article can be found here:
http://www.fishyou.com/fish-nitrates-water.php
Just sharing info that I found interesting ... what are your thoughts?
The whole article can be found here:
http://www.fishyou.com/fish-nitrates-water.php
Just sharing info that I found interesting ... what are your thoughts?
Too many people think that water change is an effective control of nitrates in aquarium. In reality, it does not and this article shows why.
The short reason why water change does not control nitrates is that you do not change 100% of your water. You only change a fraction of the total water volume, which means only a fraction of nitrates in the tank is removed everytime. If your fish always produce one unit of nitrate(be it daily,weekly or monthly) and you remove only a fraction of it (be it daily,weekly or monthly), the nitrates level will always be high.
If you didn't get that, here is an illustration
Let us imagine that 10 units (This unit is a unit of volume like mg, g etc and NOT ppm) of nitrates is produced in your tank/pond per week. The amount of nitrates produced is different for every tank/pond, depending on the number and size of fish, amount of feeding, rotting food/plants etc. You can be working with 10mg, 10g or even 10kg of nitrates but for this example we use 'units' as our unit of measure. For large fishes in ponds, you may be dealing with kilograms per week, in small tank maybe in hundreds of grams. For convenience we take our end product to be 10units.
Ok so if you are following so far, we established that our aquarium produces 10 units of nitrates per week. (We only use 'week' for convenience. If you subsitute with day or month the theory is the same.)
Now, suppose that we are trying to control nitrates using water change, and we change 50% of the aquarium water weekly (This is already a large water change, most people only change 20%-30%....
We start our calculation assuming we had zero nitrates initially..
Week 1
initial nitrates in aquarium = 0units
nitrates produced in one week = 10units
Total nitrates in aquarium = 10units
End of Week 1, 50% water change, resultant nitrates = 5 units
Week 2
initial nitrates in aquarium = 5 units (from the day before)
nitrates produced in one week = 10 units
Total nitrates in aquarium = 15 units
End of Week 2, 50% water change, resultant nitrates = 7.5 units
Week 3
initial nitrates in aquarium = 7.5 units (from the day before)
nitrates produced in one week = 10 units
Total nitrates in aquarium = 17.5 units
End of Week 3, 50% water change, resultant nitrates = 8.75 units
Week 4
initial nitrates in aquarium = 8.75 units (from the day before)
nitrates produced in one week = 10 units
Total nitrates in aquarium = 18.75 units
End of Week 4, 50% water change, resultant nitrates = 9.37 units
As you can see, as long as water is not changed out 100% (which most of us don't), nitrates will keep increasing as time goes by. Water changes does not control nitrate, but only slows down the rate of increase, normalising at the level that it is produced.