Recently I am seeing that the plants seem not to uptake NO3, as they show NO3 deficiency symptoms: the floating plants, trapa natans, have been dying slowly (green leaves, stunted growth, no new leaves, brown little spots in leaves), and only is left one, which seems to follow the same route... The echinodorus also show NO3 deficieny in old leaves (brownish, or brown areas, and thinner tissue).
I have normally 15 mg/l of NO3. Five days ago I had 15 mg/l NO3 and 1.5 PO4, one day later 14-15 mg/l (hard to precise) and 1 mg/l PO4, and next day, maybe 13 mg/l (not less in any case), and 0.7 mg/l PO4.
I see that the PO4 is being uptaken, but NO3 seems that only very slowly. Having a lot of vallisnerias, 6 ludwigias (60 cm long now), a pair of alternanthera rosanervig, two alternanthera rosafolia, ceratopyllum demersum, some egeria densa, 4 anubias barteri, and floating plants (I have also a lot of salvinia natans, which are growing slowler than expected), and seeing the levels of other nutrients I think I should have a bigger NO3 daily uptake, don't you think?
I have measured the values and they are:
CO2 = 15-17 mg/l
Mg = 7 mg/l
TDS = 250 ppm (water is 85% RO + 15% tap water, 3100 l)
Cl-= 55 mg/l
I added 0.2 mg/l of Fe twice: three and two days ago.
Today I have added Seachem Flourish for traces as per bottle indications.
The light is not easy to define as it is a garden pond, but I have done an equivalence, through lux-->lumen-->W/gal (equivalences from Tropica):
Direct sunlight (6 h): 10-13 W/gal
Not direct sunlight (2 h): 2.5-3 W/gal
Dawn & Dusk (5 h): 0-1 W/gal
As some days ago I had no Mg (or very low) I added up to 7 mg/l with MgCl2. Before adding it I had 40 mg/l of Cl-, and after adding Mg it raised to 55 mg/l.
Cl- is essential in plants to chemically balance the potassium concentration during plant breathing. On the other hand there are some papers that point to the fact that the reduction of Nitrate (to become NO2, then NH3/NH4 which the plants need), *could* be inhibited by Cl- presence (--
, it is for spinachs...), although this is for 5 times more Cl- concentration than I have.
On the other hand, I was starting to think if I had the expected CO2 really, so I have done a test two days ago:
I stopped all waterfalls to limit CO2 leakage, thus the water surface was quiet and mirror-like, after all day injecting CO2 I have not seen any change visually in plants, they were not pearling as I had expected... Then I measured the CO2 concentration.
At side of CO2 test kits, I had into the pond the JBL drop checker, which at the end of day was very dark (!) and showed a kind of blue-greenish that at best could match with 12 mg/l. The liquid was really dark.
I then tested for CO2 with two different tests: Salifert and JBL Direct. These tests have to be executed two times, one with tank water and then the blank sample (sample without CO2): tank water sample aerated 10 min (I have aerated it through all night, just in case). In fact the principle is to measure acid component of water, I think, so you have to first measure all acids, then subtract the blank result from the first one.
Salifert (5 mg/l steps):
No-aerated sample: 55 mg/l
Blank sample: 15 mg/l
CO2 result = 55 - 15 = 40 mg/l
JBL Direct (2 mg/l steps):
No-aerated sample: 52 mg/l
Blank sample: 14 mg/l
CO2 result = 52 - 14 = 38 mg/l
So, which measure reflects better the CO2 content ?
Salifert (40 ppm), JBL Direct (38 ppm) or JBL Drop-checker (12 ppm) ? I tend to believe the drop test kits, after all they use different methods/reactives, and they both match, although I can't imagine why the drop-checker is not working...aside that it is in a pond corner where there is very limited movement...
If I believe that the ~40 mg/l is more real, then I must have something in the water that difficults NO3 uptake. I don't know what can be.
BTW, at the end of day I had NO3=12-13 mg/l, PO4=0.35-0.4 mg/l, KH = 9.75 ºdKH, pH=6.8-6.85. So, NO3 is still not being uptaken, or very slowly, PO4 is being uptaken (-0.3 or -0.4 per day).
I was wondering if really I have NO3 deficiency first, and if so, what could be causing it ?
- Incorrect Ca:Mg ratio ?
- Incorrect K:Cl ratio ? Too much Cl- ?
- CO2 ?
- Other ? What ?
What do you think about it ? I have not found information on Cl- concentrations. But maybe it has nothing to do with the NO3 uptake...
I would really thank you if you could help me. Any comment also regarding CO2 measurements/concentration or NO3 limitation, etc. is really welcomed.
I don't know what can I do. I thought it could be CL- or CO2 problem but it seems not... Tx!