My tank had a high nitrate concentration at 80ppm a few months back. I did a 40g water change weekly for 2 months and it's down to 30ppm. Now I'm doing 25g weekly and dosing vinegar as well. If I can get it down to 20ppm I'll be happy
Update: Sorry folks the nem decided to crawl behind the rocks where it's impossible to get to without reaquascaping. Therefore, sale is at a halt for now. Thanks for all the interests though.