Well 44.3 ppm of nitrate measuring total ions is really not all that much. If you read the EPA link I included you will see that this is the level needed to be protective of infants.
How harmful nitrates may be to fish is a subject of much debate. Some fish seem able to handle extrememly high levels, in the 100s of ppms (on the nitrogen scale) while the most sensitive of aquatic critters Salmonids and water "bugs" seem to have issues at 10 ppms or more (most of these are not things ever found in tanks).
Here is a perfect example in an Abstract from a 2002 paper using rice fish "
Aquatic animal research in space station and its issues — focus on support technology on nitrate toxicity —"
Abstract
We studied the effects of accumulated nitrate in water on the spawning, hatching and development of medaka using a simple nitrifying filter and a combined filter having both nitrifying and denitrifying capabilities. A nitrate concentration of 100mgNO3−-N/L was clearly of lethal toxicity to fish when they were exposed to nitrate in both adult and the growing phases. A nitrate concentration of 75mgNO3−-N/L reduced the fertilization rate, delayed the hatching time and reduced the hatching rate of the eggs laid by adults and decreased the growth rate of juveniles. In addition, nitrate accumulations as low as 50mgNO3−-N/L remarkably retarded spawning and lowered the number of eggs laid by fish exposed in the juvenile phase. The effects on the reproduction system may be initiated by a low concentration, approximately 30mgNO3−-N/L.
from
http
/www.sciencedirect.com/science/article/pii/S027311770200399X
Note, the lowest nitrate value mentioned is "30mgNO3−-N/L" and on our test kits this would be about 132 ppm. That is 3 times the maximum allowable level in USA municipal water.
There is a ton of definite research on the toxicity of Ammonia to fish. There is also a lot of data on nitrite as well. However, with nitrate there is much less. The one thing we do know is that a good water change routine should hold nitrate to reasonable levels in many tanks. Those where this is not the case have to look to additional means for lowering it. The problem is knowing when this might be the case due to the inaccuracies of hobby nitrate kits.
All of this is complicated by where the potential source of nitrate in one's tap might be. Bear in mind that municipal water supplies are only regulated as long as it is in the public part of the supply system. This system stops at the interface of public and private property. So, any issues arising from things related to the private pipes etc. are unrelated to the water that comes from the public part of the system.
The reason this matter has to do with nitrifying bacteria which lives and thrives in our private pipes. Here are some studies re this:
http/www.awwa.org/publications/journal-awwa/abstract/articleid/22199.aspx
http/www.bvsde.paho.org/bvsacg/fulltext/chloramine.pdf
Basically, even if the municipal water supply has low nitrate, your private plumbing may be increasing them. I am curious from where the water you are having tested will come. Will they take it from before it enters your pipes, from your tap or from both? Please give us a report about what exactly they do and what the results are. For the sake of interest, you might want to ask them for a small amount of water from each place they take it so that you can test it using your nitrate kit. Then you can compare those results to the ones which are reported by the professionals.
