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The only way to quickly lower nitrate levels is to perform water changes. Denitrification units can be used to reduce nitrate levels when the tank cycles but is very costly. Water changes are the best and easiest remedy.
I recommend staying away from the AZ-NO3 product! I did some reading on it, tried it and had the same results several others reported, massive attack of red cyno bacteria after using it for several weeks. My tank was pretty mature and was well past the typical cyno problems that almost always effect a tank sometime in the first 6 months. It took me several months to eliminate the stuff after using the product. Additionally, I saw no nitrate lowering benefit. I admit to discontinuing the product abruptly but only after the cyno was evident.