Post
by Keith Wolcott » Sat Jan 29, 2011 7:46 am
Sorceress- Even a year with happy healthy fish is no guarantee that you are not headed for trouble. The nitrate level can very slowly increase and the fish will adapt to it as much as they can, but at some point it will become a problem. If your fish load is small and you have lots of plants, you might be fine.
If you are interested, here is some data. My tanks have about an average fish load and I find that this adds about 1 ppm per day of nitrate (from the food put in, which the fish eat, excrete as ammonia, which bacteria transform to nitrite, which bacteria transform to nitrate). Below, I did calculations (actually I just used the water change wizard that ChefKeith and I wrote) for fish loads of .5, 1, and 2 ppm per day of nitrate added. The first is a very low fish load and the last is quite high, but some people have such tanks. Now suppose the nitrate starts at 10 ppm and you do 50% water changes every month. Below is what happens over time in each case.
Case 1: A low fish load adds .5 ppm per day of nitrate.
At 1 month, right after the water change, the nitrate will be at 14 ppm.
At 6 months, right after the water change, the nitrate will be at 20 ppm.
At 1 year, right after the water change, the nitrate will be at 20 ppm.
At 2 years, right after the water change, the nitrate will be at 20 ppm.
Thus the nitrate plateaus at 20 ppm right after each water change. Just before each water change, it is 40 ppm.
Case 2: A medium fish load adds 1 ppm per day of nitrate.
At 1 month, right after the water change, the nitrate will be at 23 ppm.
At 6 months, right after the water change, the nitrate will be at 40 ppm.
At 1 year, right after the water change, the nitrate will be at 41 ppm.
At 2 years, right after the water change, the nitrate will be at 41 ppm.
Thus the nitrate stabilizes at 41 ppm right after each water change. Just before each water change, it is 82 ppm.
Case 3: A heavy fish load adds 2 ppm per day of nitrate.
At 1 month, right after the water change, the nitrate will be at 41 ppm.
At 6 months, right after the water change, the nitrate will be at 79 ppm.
At 1 year, right after the water change, the nitrate will be at 82 ppm.
At 2 years, right after the water change, the nitrate will be at 82 ppm.
Thus the nitrate stabilizes at 82 ppm right after each water change. Just before each water change, it is 164 ppm.
I would consider that in all three cases, not only is the nitrate rather high, but also the water change is hard on the fish since it there is such a large change in the nitrate levels. Again, only a nitrate test kit can tell you what is really happening in your case.