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Algae and PMDD

Mike Charlton wrote:

> I'm having a hard time keeping my nitrate levels at a measurable level.
> Lately I've been adding 5 ml of 0.5 molar KNO3 to my 180 liter tank
> per day (about 0.8 ppm NO3).  This seems like alot to me.  I'm using
> aquarium pharmaceutical's nitrate test.  Is it perhaps faulty?

I've used several nitrate test kits in the past few months and the only one
I've come to trust is the Lamotte (thank you Steve Dixon for not saying "I
told you so").  The only test kit on my list that I didn't get to was the
Salifert NO3 kit.  At any rate, you know the precise amount of NO3 available
and it should be pretty simple to test your kit.

> I've also been trying to measure my phosphate levels.  Unfortunately my
> AP phosphate test is vitually useless. I seem to have less than 0.5 ppm
> phosphate, but I'm not sure that this information is useful to me :-).

0.5ppm is a high PO4 level, perhaps an order of magnitude higher than you
want in your tank.  My own experience with the AP kit ended when I threw it
out in disgust after borrowing a friend's Hach kit.

> So after all that preamble, I'd like to get some advice.  Should I assume
> that my plants are still nitrogen limited and that the increased algea
> growth is due to the fact that I have been adding nitrate while there is
> still lots of phosphate in the water?  Or should I assume that my test kit
> is faulty and cut back on the nitrate (If I've done my math right, I'm
> currently adding 10 times the suggested amount)?

I ran my tank full-blast for almost two months before I was able to test Fe,
NO3 and PO4 accurately, and it never looked better.  I had over 50ppm NO3,
.7ppm Fe and 0.0ppm PO4, never saw a hint of algae and the plants screamed
for more.  I even had placed a large number of Jobes plant sticks into the
substrate during this period, before friends gently explained to me that one
or two sticks were a lot, and that I should be prepared to start large water
changes on a daily basis.  In my case, both the substrate and the water
column were chock-full of NO3 and I fared well.  Suffice to say, I've calmed
things down a lot since those heady days, but I keep a careful log and watch
what I'm doing.

So here's my advice:
1.  Get your hands on NO3 and PO4 test kits that you can trust.
2.  If you have over 0.5ppm PO4 AND under 5ppm NO3, CAREFULLY add a little
KNO3 and test some more.  I should stress that other environmental
conditions must be right before you start adding nitrate.  This includes
lighting, GH, CO2.  You're probably nitrate-limited, when you want to be

michael rubin
michael at rubinworld_com