Maiden's hair plant useless?

[mansiz]

Hmm, I placed a maiden's hair plant (turtle grass) few weeks go, around 3 weeks, but my NO3 level remains the same, is it useless in reducing NO3? Or it needs a large quantities in order to works?

 

[nodoubt471]

how big is your tank? if its a large tank, you probably need a few to actually reduce the nitrate level.