I have a 30 gal. tank I started around 9/19/07. It's one of those tall skinny tanks about 4 feet high. I have about 12 fish in right now. My Amonia is always 0 and my Nitrites are always 0, but my Nitrates are like 80 and my PH is about 8.0. I can't get my Nitrates to go down. I've been doing 5 gallon water changes, and it goes down a little bit but not much and then goes back up higher. I've been putting in the Kordon NovAqua Plus and AmQuel plus products, but it hasn't been lowering the Nitrates. Everytime I put in the Kordon stuff it lowered my PH about 5 points. I did it twice and it lowered it to like 6.7. My alkaline was like at 60. So, I used Alkaline Buffer to raise my alkiline but it also raised my PH to like 8.0. I tried using the Kordon but it will no longer lower my PH. I tried using Neutral Regulator, but it won't lower my PH either. I add aquarium salt to the new water before I put it in the tank when I do a water change, and I add Cycle every week for maintenance. I change the charcole filter about ever 4-6 weeks. I try to do a 5 gal water change every 2 weeks with filtered water from my water filtration system. Please let me know if you can help me resolve this issue. I can't add anymore fish because they don't last more then a couple of weeks and then die. I guess because of my Nitrate and PH problem. Thank you for your help and time!