my tank has been up for a month but no fish .... i used live sand and have 30 pounds of liverock ,,,,,,its a 55 gallon tank ... 2 days ago the pet store said i could not put fish in it the nitrate test came back purple ....i bought a kit so i could test it myself and it came back at about 10 to 20 ppm ..... can i put fish in it or no ,,,,,,,thanks