Struggling to Keep Nitrates Up

[Ben_RF]

I am concerned that I am not properly taking care of my plants in my 35g hexagon tank. I have one tank that I absolutely struggle to keep nitrates above 5 ppm.  It is my 35 gallon hexagon tank with a 1/2" base of peat moss with 2" of ecocomplete on top of it.  The background plants are Amazon swords (4) which are growing somewhat slow.  The midground plants are broadleaf sagittaria (4).  What makes up the front half of the tank is dwarf sagitaria.  Both types of sagitaria is growing very well.  In the 6" ring at the top I have frogbit which I weed back twice a week.  At the moment, based on the calculation of rotala butterfly I made my mixture of KNO3 to be a dosing to reach a target of 7.5 ppm and dose 4x a week.  The dose is detectable throughout the day of the dosing, however it is depleted by the next day.  I do use passive CO2.  Algae is not a problem. I have for about a year I have put root tabs in the substrate at the beginning of the month as the bulk of the plants are root feeders.  I use 10 root tabs at the beginning of the month (at the moment DIY osmocote root tabs that I made in bulk then hope to switch to the co op brand).  

Should I be concerned about the low levels of nitrate in the water column and begin dosing more?  Or because I do dose heavily in the substrate, I shouldn't worry about it so much?  

Edit:  The dosing seems to be accurate and not miscalculated based on my usage in my other tanks. 

Edit:  I have cross checked these levels with three different types of test kits.  The readings seem to be accurate.

Edited September 14, 2020 by Ben_RF
clarity

[Ben_RF]

If stocking is relevant:

1 dwarf gouramis
25-30 something neon tetras. 
5 guppies temporarily homed for a friend until they are able to replace their tank.
5 fat and happy otocinclus. 
A small amount of rams horn snails. 

This tank was previously planted different with the inhabitants, and a year ago I tore it down and replanted. 

[Seized]

Id suggest using easy green to boost plant nutrition.

 

[TheDukeAnumber1]

Too low NO3 can cause plants to start growing slowly with pale leaves and start losing older leaves prematurely. If your concern is just as you said "proper care", let your plants tell the story. If you are after faster growth I would test an increased dose.

Edited September 15, 2020 by TheDukeAnumber1

[Cory]

 You  may need to put more root tabs under the amazon swords. I've had them eat 10+ root tabs for 1 large plant every month. As far as keeping nitrogen up, it looks that by testing your plants are consuming it. One thing I'd mention is that you're dosing kno3, however without the other building blocks you won't get optimal growth if you are lacking other nutrients. This is why fertilizers are typically more than just KNo3, as plants need a range of nutrients to grow. 

[Daniel]

Plant growth is limited by the scarcest element. The classic illustration is that of a leaky barrel. In this illustration it doesn't matter how much of any other element you have, plant growth will always be limited by nitrogen since that is the lowest stave in the barrel, i.e. the limiting nutrient.

 

Edited September 15, 2020 by Daniel
*Leibig's Law

[Ben_RF]

Thank you all. I truly appreciate all your feedback and input

 

 I do dose with the KN03 the following: Mono Potassium Phosphate (KpPO4), Potassium Sulfate (K2SO4), and Magnesium Sulfate (MgSO4).  I also dose Plantex CSM + B for my micros.  Our water here is not liquid rock, but it is hard with a wide spectrum of minerals in it. Ph with the balancers from the city in the water comes in around 7.1 then after the balancers wear off it comes in at 7.5. 

Perhaps I have to many amazon swords and should ween then down. Maybe thats where all my nitrates are going.  I could also remove the few frogbits I keep in the corral in the tank. 

Edit: Maybe I should also increase the amount of root tabs or frequency of root tabs?
 

Edited September 15, 2020 by Ben_RF

[NordernAquariums]

I don't know, I am just curious, would the peat moss be absorbing the nutrients/nitrates?