I just noticed that the nitrate level in tap water that I dechlorinate and set aside for my next water change drops over the course of a few days. I have verified this through repeat testing. Water I tested a few days ago right out of the tap came in at 10ppm nitrate. I used this same water to fill a 5 gallon pail and declorinated it as I usually do. Today I tested this water and it came out below 5ppm. Can anyone explain this?
I think I've heard the same however I don't believe it's suppose to happen that quickly. My understanding is that it is released this way in very small quantities. One of the reasons why frequent water changes are required is to keep nitrate levels down.........still a bit baffled,
Nitrate is only one of the reasons for water changes as you mentioned. The drop in nitrate test results you saw could be caused by several factors. To run a few ideas off that you may be able to dismiss... 1. Light, if the water is stored dechlorinated in a lit area photosynthetic bacteria or algae may start to use the nitrate long before water starts to look green. 2. Temperature, water out the tap is generally cold but will warm after a few days stored in the house. This may effect test results. 3. Anaerobic Activity, if the water goes stagnant anaerobic bacteria grow that will accelerate the breakdown of nitrate. Bubbling fresh air through the water will kill this bacteria releasing the nitrate back into the water. 4. Settling - Solid matter could be settling to the bottom of the storage tub, did it get mixed up before a sample was taken? 5. Nitrate Tests - hobby nitrate tests are normally not very accurate, especially in the lower ranges. It might be just fluke.