why do I need so much NO3 ?

[Aviss]

Hi everybody,
first of all i want to congratulate this great forum for all the useful information that I found about planted tank.
I hope you can understand my english, otherwise I can try to use google traductor.

I have a 430 l. (113 gallon) planted tank with low light (3 x 36w t8) and high CO2 (the drop checker is light green
and the the table KH/pH give me 70 ppm of CO2).

The question is this :
I dose weekly 25 mg/l of NO3 and 3 mg/l of PO4 after water change.
I test No3 and PO4 before water change and it seems that very little of these ferts are used. The tests give me
25 mg/l of NO3 and 3 mg/l of PO4.
I know that this fertilization might seems high for a low light tank, but if I try to reduce the No3 to 10/15 mg/l
my crypts start to become yellow and then melt and the leaves of the other plants turn to very pale green.

I can't explain the reason of this. Maybe the CO2 is too high for a low light tank ?

Regards.

 

[dutchy]

Hi,

CO2 is never too high for plants. Plants can use up to 10000 (!) ppm of CO2. We are never able to supply that. The only limit to CO2 is the fish we keep.

To me it seems like the tests you use to measure NO3 are wrong, or, fairly inaccurate. probably your 10 ppm measurement is more like zero. But why bother to measure? If you dose high enough there's no need to. Many EI users don't measure.

 

[Aviss]

Hi dutchy,
thank you for the reply.

I agree with you that tests may be inaccurate.
I don't have any problem to add 25 or more mg/l of NO3 but, just for desire to know, I want to understand why in my very low light tank I have to
dose an amount that generally is needed in high light tank.
I don't have fast growing plants and I feed regularly my fish.

Here you can see the tank.
http://showcase.aquatic-gardeners.org/2012/show284.html

My thought is that the CO2 at this high level stimulate very much the growth of plants, more nutrient is needed and
so it seems I must treat this tank as a high light tank.

 

[dutchy]

My thought is that the CO2 at this high level stimulate very much the growth of plants, more nutrient is needed and
so it seems I must treat this tank as a high light tank.

Very well thought I must say. Good CO2 drives plant growth at a significant amount. Nice tank btw.

 

[Aviss]

Nice tank btw.

Thanks dutchy.

Just to compare with my dosing, can you please tell me how much no3 you
add in your 180 gallons weekly ?

 

[Tom Barr]

This tank is using a lot of CO2. You do not need to dose that much NO3 likely.
Not that doing so.... would hurt............

I'd focus on CO2 and consistency.

You can adjust CO2 up (or down) very slow and carefully.
Then, observe the plants.

 

[Aviss]

Ok Tom,
I will try to change the CO2 amount and see what happens

Thanks,
Paolo.