N ppm < 1 despite macro ferts added ???

[jfravn]

Hi,

I run a 182 litre high-tech planted tank. I add daily micro and macro fertilizers with the following macro target ppms:
N: 22
K: 33
P: 4,5
M: 12

Despite these targets I measure my nitrate value to less than 1 ppm, which basically means that my plants either 'eat' all there is or have nothing to live from. There is only limited pearling and growth is not at the levels where I would expect them with my setup. Old leaves on staurogyne repens turns yellow with GSA.

Tap water values: GH 19, pH 7.6

Additional tech specs are:
Filtration: 2 x Eheim 2075 (1250 litre/hour each; effectively 700 litre/hour each= around 10 x water change per hour)
Light: Arcadia OT2 Luminare 4 x 39W - Giesemann Midday 6000K and JBL Natur 9000K
CO2: Pressurized through cheramic diffusor lowers pH to 6,7

I am wondering whether my intense biological filtration 'kills' the nitrate. Should I replace the biomech biological material in one of the filters with purely mechanical filtration?

Here is a picture:

Any thoughts?

 

[ceg4048]

Hi,

I run a 182 litre high-tech planted tank. I add daily micro and macro fertilizers with the following macro target ppms:
N: 22
K: 33
P: 4,5
M: 12

Despite these targets I measure my nitrate value to less than 1 ppm, which basically means that my plants either 'eat' all there is or have nothing to live from. There is only limited pearling and growth is not at the levels where I would expect them with my setup. Old leaves on staurogyne repens turns yellow with GSA.

Tap water values: GH 19, pH 7.6

Additional tech specs are:
Filtration: 2 x Eheim 2075 (1250 litre/hour each; effectively 700 litre/hour each= around 10 x water change per hour)
Light: Arcadia OT2 Luminare 4 x 39W - Giesemann Midday 6000K and JBL Natur 9000K
CO2: Pressurized through cheramic diffusor lowers pH to 6,7

I am wondering whether my intense biological filtration 'kills' the nitrate. Should I replace the biomech biological material in one of the filters with purely mechanical filtration?

This is unlikely. Filters bacteria generate NO3 by oxidation of ammonia. NO3 is the end product of the nitrification cycle. Therefore more filtration should mean more NO3, not less.

It's a very bad idea to get hypnotized by target ppm. You compound your problems by trying to measure them with test kits which are notoriously unreliable. This is precisely why you have this conflict.

Now certainly, it could be that your tank consumes NO3 at a high rate. If CO2 and flow are in good shape then the Nitrogen assimilation is accelerated. Under high lighting such as you have the N uptake demand is massive.

You should only set your target ppm by a stoichiometric analysis and dose the values you compute. Based on your feedback from the plant growth performance you should then make the adjustments. Yellowing of old leaves is a pretty good sign of N deficiency so you should increase the NO3 dosage, however GSA is a sign of low P (if CO2 is confirmed to be good) so you'll need to improve the PO4 dosage.

As plant biomass increases so does the demand for nutrients/CO2, so we should expect that the dosages we start off with at tank setup will be insufficient months later as the mass increases.

That's a gorgeous tank by the way. Beautifully executed.

Cheers,

 

[jfravn]

It's a very bad idea to get hypnotized by target ppm. You compound your problems by trying to measure them with test kits which are notoriously unreliable. This is precisely why you have this conflict.

You should only set your target ppm by a stoichiometric analysis and dose the values you compute. Based on your feedback from the plant growth performance you should then make the adjustments. Yellowing of old leaves is a pretty good sign of N deficiency so you should increase the NO3 dosage, however GSA is a sign of low P (if CO2 is confirmed to be good) so you'll need to improve the PO4 dosage.

That's a gorgeous tank by the way. Beautifully executed.
Cheers,

Thanks! I know that I shouldn't rely 100% on test kits, but as a beginner it can be difficult to read everything from the plants themselves. That's when I doublecheck my observations with a test kit. I know they are not reliable, but when they show ppm less than 1, its probably not near the target of 22...

I have increased micro and macro ferts a bit and is currently waiting for the effects!