Okay so here it goes. I’m not a “noob” per say but I’m trying to figure something out. I have a 75 gallon tank that I have had a fluval 406 running on it for a month or so, before that on a 29 gallon for a few months so it was plenty seeded. I recently got a fluval fx4 that it is running in tandem with the 406 on the 75 gallon so I can get it seeded to put the 406 on a 55 tank. My readings are always 0-amonia 0-nitrite And here’s the issue 5-20 nitrate. Maybe sometimes higher. I just did a 35 gallon water change yesterday and a 20 the day before that, dosing with prime and even 5x dosing on the larger water change. My nitrates are still there and seem to stay the same. Should I use my seachem stability to do the “new tank set up for 7 days” or what do you guys think is going on? The fx4 I got from a girl who had it on a 125 for 2 weeks before she was told to get rid of her 125 by her landlord. I hope this all made sense. I just want to know what is going on. Any suggestions???? Anymore questions just ask! OH! I have one fish in the tank, which is an Oscar around 6”. I don’t know if I should take the 406 off and run the fx4 and treat it as a “new tank” and put the 406 on the 55? Or what?