Can't take Nitrate Down (40)

[clownman]

Ok, its been like 3 weeks since I can not take my nitrate down!!
I am doing regular water change (as a matter of fact, I have done it back to back 3 days a week last week). But my nitrate is at 40
Its a 37 Gallon Tank (Reef wanna be)
5 months almost since it has been established (could be little here and there). I only have two fish in it right now (a scopas Tang, who need to be moved as he's getting really big and not meant for this tank) and a Percula Clown.
I have 20 Hermit, 10 Tarbo, 1 Emerald and various other critters that I discover every now and then. Right now, I have some button polyps coral and some zoanthids on liverock.
Every time I do test,
pH 8.2
Nitrite 0
Ammonia 0
Nitrate 40
Some nicelooking rock which were growing some cool purple.../reed algae are quickly turning green. Corals are looking healthy (I think they've grown a little since I got some frags), fish are looking healthy, critters are every so much busy. I don't see now sign of distress but in me. (except, I see that green algae taking over)
I don't want to use any Chemical if I can avoid. I have been however, using B-IONIC as I got those two pair gallon for free from somebody. Not sure if that doing it? I am applying very little almost everyday as per the instruction.
I also provide the coral frag DT's Phytoplankton which initially was my suspect as the live plankton in it is green.
Anyway, if I could rate my tank right now, beside green growth and Nitrate, I would say, it is not bad.
Can anybody help me understand how can I get nitrate down? Only water change? Not working though
Best Regards
Clownman

 

[y2says]

What kind of filter system are you using?

 

[clownman]

50+ Fiji/Florida rock mix
3-4-5" DSB (Livesand)
Hang on Protein Skimmer/Filter (forgot the name)

 

[ironreef]

Try another test kit of have 2 diffrent lfs test see it the test are accurate

 

[kris walker]

Were your nitrates ever 0 before 3 weeks ago? If not, maybe the regular water changes you are making have been interfering with a nitrate colony from establishing itself in the anaerobic parts of your liverock.
sam

 

[clownman]

It was 10 before and I wasn't worried about it. Don't recall it being 0 ever.
I will try a different test kit that I have at home tomorrow.
Having LFS test it? I am always doubtful the way they handle things. Let's just say, I don't have any high confidence on my LFS

 

[tomato clown]

This may sound kinda dumb, but are you using your test the proper way? Reason I ask is because when I was testing for different levels 1 day I managed to either confuse the drops, or I may have mixed up the bottles. I redid my test after I went to my lfs with it and they said it was fine, and my test read normal.
Dan

 

[clownman]

I have been doing constantly and only Nitrate seems to be the high mark. Since back to back Nitrate staying at 40, I am doing test even more carefully.