Nitrate deficiency

Hi everyone,

I've been noticing that every time my nitrates get down to zero in my
planted tanks I get a yucky brown slimy sludge growing.  I'd like to
know if anyone else has encountered this.

I've also been having problems keeping my nitrates up!  My tanks are
fairly well stocked but nitrates keep dropping to zero.  I have recently
tried adding a nitrate containing fertilizer (Plant Tabbs) but these have
more phosphates than nitrogen.  I had to add 6 to my 25 gal tank to get
up to 3 ppm nitrate but that went to zero the next day.  In the meantime
I now have about 0.8 ppm phosphate - no algae bloom yet & I'm keeping
my fingers crossed.

I have decided to add just some calcium nitrate (Ca(NO3)2) and some
potassium nitrate (KNO3) along with some magnesium sulphate (MgSO4) -
basically Hoaglands Solution without the potassium phosphate (I will
double the amount of potassium nitrate to get more potassium).  I have
ordered these chemicals from a chemical supply company (Sigma).
Does anyone forsee a problem with me doing this?  or can you suggest
any other solutions? (I'm already overfeeding my fish).