[aviel]

Hi,

On the last 10 days or so I noticed that nitrate/phosphate levels in my tank wouldn't drop like it used to. I tended to relate that to the fact that my CO2 levels dropped to ~15 ppm (from ~30 ppm) during this period without me noticing that. There was(is) also a slight BBA problem just because of that co2 shortage. Anyway - I fixed that 4 days ago, targetted no3=15 ppm and po4=4 ppm and dosed 2 ppm nitrate daily through KNO3, and 0.35 ppm phsophate through KH2PO4. I was expecting the nitrate to drop down from 15 ppm. Yesterday I tested and was suprised to find out that my nitrate levels crossed the 20 ppm and the PO4 exceeds 2 ppm. I have 2.5 wpg, I add (more than) enough iron+trace, I even added 10 ppm K at water change through K2SO4 - So really I don't see a reason for this.

My guess is that during the low CO2 period there was excess of iron/nitrate in my water column which plants couldn't use. They stored it and now that CO2 is back, still they are not hungry yet, hence the high levels.

Makes sense? Or maybe other explanation for this rude behavior of my water chemistry?

Aviel.

 

[aviel]

Oooops I am so sorry,

I am targetting PO4 = 1.5 PPM - not 4 PPM.
No need to add Ca, Mg - tap water is ~17 PPM GH so I have to mix with RO.
I dose 2.5 ppm Fe per day - I did a short survey and that's what folks are dosing these days.
Plants look fine - Macrandra doesn't look good enough.

And my question was actually - if I do provide with all the necessary nutrients - is it that it still takes time for the plant to first deplete it's own reserves before consuming nutrients from the water column? Is it true that when CO2 was low the plant couldn't use as much nutrients for photosynthesis and therefore stored it and therefore now doesn't need new nutrients from the water column? Hence low consumption rate?

Aviel.

 

[aviel]

I think I have an idea why my NO3 doesn't drop like it used to...

I think that I added fish to the point that I have 1.15 inch per gallon which means more ammonia and therefore plants no longer need as much KNO3.

It means that I have now to start dosing more K. Since I don't have a potassium test kit my logic says the following: If NO3 eating rate was 3 ppm per day and now it's only 1 ppm per day then 2 ppm per day are added daily through fish food. This means that still my consumption rate of N is high and actually since I dose much more po4 lately - it should be higher - say equivalent to 4 ppm NO3. Now K should be the limiting factor - I should then dose K that I used to through KNO3 - K is 60% of N in KNO3 so I have to dose 1.8 ppm K ((4-1)*60% daily. I intend to add K2SO4 for this.

Does this make sense?

Also - even though there's more fish now in my aquarium - really I don't throw ounces of meat in there - and food should be the sole source of nitrogen - no? So where is this N coming from?

Aviel.

 

[aviel]

Hi,

After discussin this with Tom Barr here (http://www.aquaticplantcentral.com/forum/viewtopic.php?t=2822&start=15) I fill that there's just no way food shall cause this uptake problem. I really don't feed that much. But on the other hand N updatke is almost stunted...

po4 level is constant @ 1.5 ppm is I dose 0.35 ppm daily - this is a hard riddle. How on earth po4 levels drop so significantly while NO3 levels don't???

Here's what I could suspect -

1) As I said - I had 2-3 weeks with only 15 ppm CO2 before I raised it back to 35 ppm. So maybe when the plants were CO2 limited they were storing the N and now they still have it and don't need to take it from the water column.

2) La motte test kit read N=4 which translates to NO3 = 17.6 ppm - but maybe it measures non available NO3??? Maybe the available NO3 is real low?

3) I stopped dosing ferrous gluconate but still am adding 0.25 ppm worth of iron from slow Fe base (50% CSM + 50% Iron chelate). Maybe with slow Fe dosing that much doesn't make sense because iron builds up to toxic levels. Also CSM contains micros and if I add daily micros "equivalent" to 0.125 ppm iron then probably that again is too much. On the other hand I believe the UV breaks the chelate so it shouldn't really pile up. Right?

4) When I corrected the levels of CO2 there was a drop in PH which killed the filter bacteria. So plants are fludded now with NH4 and just are not in the mood for scavanging NO3 when there's abundant NH4... Anyway my NH4/NO2 readings are 0 !!!

Anyway - I need a quick help here. This is a 2-2.5 wpg tank, with CO2 and everyting and if something goes wrong algae will sooner or later attack!

Thank you so much,

Aviel.