Although I use Seachem liquid ferts on my 10g. Plants will use up the available nitrates quickly, and low to non-existent nitrates aren't uncommon in heavily planted tanks.
yeah, if you have very little nitrates, your plants will start looking a little bad. I had the same thing happen to me, a number of plants never recovered. About the only plant I have left from my first attempt is my java ferns LOL.
0 nitrates are just as bad for planted tanks than 80 nitrates in a non planted.