Nitrates. Help!

Question
Christy, I am about to despair.  I have had a 60 gal hex for about 15 years and due to some medical and house-sitter problems the tank hit major "old tank syndrome" and almost everything died (the tank had an underground filter plus a 3 stage AquaClear hang-on-the back of the tank filter).  I have spent two and half years, with no fish and no plants, getting the tank cleaned up, including getting an AquariPure denitrifying system.  I had the tank planted and the nitrates down to 40 ppm (Ammonia & Nitrites 0 and all other readings fine).  I got a gravel vacuuming system, did a couple 20-25% water changes with vacuuming, and had the nitrates down to 20 ppm.  I was waiting to get the nitrates down to 15% before starting to re-stock (I don't want them much lower than that for the sake of the plants), did another 20% water change with vacuuming, and the nitrates are back to 40 ppm!  I have about a 3" gravel base and currently have one fish in the tank, a Chinese algae eater (I thought the denitrifying filter would work better with something stirring things up a bit). My tap water has nitrate levels off the chart, so I need filtered water and that makes water changes of more that 25% problematic. What am I doing wrong?  How can I get my nitrates to 15 ppm?

Answer
FOLLOW UP:  
Hi Eleanor
I was just reading through a forum, and came across someone that had kind of the same situation, nitrates out of the tap were reading 40 ppm.  It's kind of a long post on there, but the guy talks about an RO unit he bought that removed the nitrates from the tap water...anyway, thought of you, here's the link, hopefully it'll work:

http://www.oscarfish.com/discussion/high-nitrates-out-of-tap-vt69090.html?highli...


Hi Eleanor
A few years ago, they(fish forums and such I was involved with) were recommending keeping nitrates under 40 ppm.  Now, within the two years or so, they've recommended under 20 ppm.  I only mention that because I think it's interesting that 40 ppm was ok 4 years ago, but now it's not...obviously the lower you can get them, the better which only makes sense.

Now I'm not familiar with the AquariPure system, so I looked it up.  Sounds pretty interesting!  I can't say for sure, since I'm not familiar with the product, but I don't like the idea of not doing as frequent water changes, like the site mentions.  Water changes on top of removing nitrates(except in your situation with high nitrates in the tap), it adds needed minerals to the water that the plants and fish need.

One thing I think may help, you won't like it though :) remove the under gravel filter.  Especially if it's been in there awhile, they tend to trap a lot of uneaten food and fish waste under there.  That would cause your nitrates to sky rocket.  Especially if you did a water change and stirred all that up.  

Another thing, what kind of test kit are you using?  I recommend using the liquid dropper test kits as opposed to the dip stick test kits.  The dip stick kits just aren't as accurate, and if they go bad/expire, they can give you false readings as well.  

Can you at least do 25% water changes once a week with the filtered water?  Or even two water changes weekly of about 15%?  That would help a lot in reducing the nitrates.  If you're not adding the tap water, then I don't understand why the plants and that denitrifier aren't working to lower them, unless it's like I said the under gravel filter.  Did you fill up the tank with the tap water?  You may need to do a larger water change, then get on that once or twice a week schedule.

So, I'd remove the undergravel filter, do a water change-vacumming really good-with the filtered water in conjunction with it, let it all settle down a bit then retest and see if that helps any.  Another thing, that 3 inches of gravel, is that for the plants I"m guessing?

Christy