nitrite levels over time

Question
I have a 185 gallon all-glass aquarium that I have had in operation for 12 years. It has a wet-dry filtration system, a venturi skimmer, and a UV sterilizer. I am using crushed coral for substrate, and I have several pieces of various corals for the fish to hide in. The pump's volume is around 1100 GPH. I have allowed algae to grow over the back glass, as the fish seem to like to eat it.  

My problem is this: regardless of how much water I change out, and using quick dip test strips as a reference, I cannot get nitrate levels below 10 ppm to save my butt. I have damsels, wrasses, tangs, and a hediodonicus, some of which are almost four years old. But angels or butterfly fishes can't stand it for long and swim off to the great beyond soon after arrival.

Am I going to have to break the whole thing down and clean it all out and start over, or am I overlooking something?

Answer
Lavon,
Nitrite or nitrate?  Your subject said one while your question referenced the other.  I'm assuming your talking nitrate.

That being said, there are a few things that I would look at before deciding to tear down.

1)  What type of water are you using for your water changes?  If it's tap water, test that water for nitrates or other organic waste like phosphate.  You may want to do these tests with a better quality test than a dip strip.  Those things are convenient, but just are not reliable.  Clearly if your source water has nitrate in it then doing water changes can be pretty counter productive.  Also, how frequently are you doing these water changes?

2)  What condition is the substrate?  When you do your water changes do you find a lot of debree in it or is it pretty clean?

3)  Wet/Dry filter biological chamber.  What type of media are you using?  Do you notice a lot of debree inside this chamber?  It's not uncommon for these to go unchecked and allowed to accumulate debree that eventually becomes a nitrate haven.

All that being said, a nitrate level around 10 ppm in a fish only system is not terrible.  Anything over 40 and I would be concerned, but 10... most people I know wouldn't know what to do if they had a level like that.  They'd honestly think the water test was wrong!

Best of luck with your tank!

Regards,
Scott Johnson
Aquarium Crazy Fish
www.aquariumcrazyfish.com