[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Phosphate/Nitrate use by plants

I did some testing on tanks the other day and I've been pondering the results.

I'd presumed that a tank with higher nitrates would also have higher 
phosphates, as they would be similarly utilized in a tank. Up until 2 months 
or so ago, I didn't even own a phosphate test kit.

True to this theory, a tank where I run CO2 on had about .1 ppm phosphates 
and < 5 ppm nitrates. This made sense.

A low-light tank, with no co2 and working on heavy plant coverage, nitrates 
ran approx. 12 ppm, with phosphates in the 1-2 ppm range (not easy to read 

I tank that contains lots of water sprite, hygrophila difformis, java & 
willow moss, and just a small bit of crypt willisi & java fern & light fish 
load had < 5 ppm nitrates, but surprisingly high phosphates, off the scale (> 
2 ppm). 

2 10 gallon tanks were a surprise to me.  One has a very light fish load, 
heavy coverage with pennywort  and approx. 0 nitrates. Phosphates were off 
the scale, > 2 ppm. The other 10 gallon has a heavy fish load, various plants 
w/light to medium coverage, lots of fur algae growing, and approx 15 ppm 
nitrates, but phosphates were approx. 1 ppm.

Feeding is basically the same in all, but varies only according to fish load, 
a mix of live, frozen, flake. Fish load is different, as mentioned above. 
Plant mass varies.

But the discrepancy is the nitrates and phosphates. They are obviously not be 
utilized similarly. Do plants uitlize nutrients differently? under different 
Why do tanks with a light fish load and predictably low nitrate levels have a 
high level of phosphates?

And with discussions lately about water changes, I'm wondering if high levels 
of phosphates aren't as stressful as high levels of nitrates.

Any ideas about this?


            Phosphates      Nitrates
10 gal         > 2.0                0
10 gal          1.0               15
20 gal       > 2.0              5
29 gal          0.1          < 5
55 gal       1-2                   12