One thing to consider: your water supply may have had some nitrates in it when you did your last water change. Have you checked your tap/well water for nitrates lately?
dw1305 wrote:It is difficult to test NO3 accurately,
Yes and no, if the test indicates you have some nitrate you probably do, but you can't really go a lot further than that. One reading of 50ppm is not the same as another of 50ppm, and may in reality be a much higher level. My suspicion would be that often test results of 10 or 20ppm are really an order of magnitude too small.does this mean that our NO3 tests are useless?
What is the "duckweed index"?
I like to keep low nutrient levels in my soft water planted tanks and I use a conductivity meter and the colour/growth of Limnobium and Lemna as indices of this. If I have small, slow growing, pale green floating plants and a conductivity of about 100 microS, I know water conditions are pretty good."
I use the reduction of BOD (Biochemical Oxygen Demand) concept for tank water management, rather than saying something is "good" or "bad", you look at each item in terms of what nutrients it contains, how readily available they are, and how much effect it will have on BOD. A slice of sweet potato, or a prawn, will have much more potential to pollute than a much, much larger piece of wood, this is because they have readily available, soluble sugars and protein, that the wood doesn't, and therefore a higher BOD."
You really need to know the range of NO3 levels, the legal limit is 50ppm, but a lot of water companies often exceed this in the spring & early summer when a lot of nitrogen is being applied to silage & arable crops.I had a report from the local water supplier and they say their water is on average P.H. 7.6 Nitrite 0 and Nitrate 17.07 mg no3 / l.
I just wonder if it was a one off dose of bad water when I did a change.
Users browsing this forum: No registered users and 2 guests