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Solufeed TEC-SF usage experience

Joined
31 Aug 2020
Messages
76
Location
Cambridge
Hello, I would like to share my experiences with using of the Solufeed TEC-SF as the main micro fertiliser. It's quite attractive as it is quite cheap and it has Iron chelated by DTPA which means high PH range stability. It also has quite high levels of trace elements comparing to the mainstream micro fertiliser, especially high in Manganese and Zinc.

First, I have used it as a sole source of Iron + TE, but I found two major problems. The first one was that due to high level of TE my normal dosing of 0.5ppm of Fe per week was a bit high for some plants (e.g. I've lost my Toninas). The second issue was weird: I have mixed like 1L of micro with some ascorbic acid but after like 1.5 months I've found two things - there was some insoluble remain in the bottle of micro and the iron test has shown 0 Fe. Also, the water after dosing this mix got lime colouring, which was not very pleasant. It seems that Fe-DTPA was somehow destroyed. I used transparent bottle but I have stored it in the dark place, so I'm curious was it photodegradation or something else? Initially, Fe test (JBL) has shown good amount of Iron in this mix, but after 1.5 months it was depleted to zero.

Hence, I have decided to change micro by adding like 0.3ppm Fe on this mix + 0.1ppm Fe on FeEDDHA (also from Solufeed). This mix works just perfect for the plants and it stopped all issues with melting/chlorosis:
JPEG image-C3804C169498-1.jpeg
JPEG image-4A2A1C2EE283-1.jpeg
But there is one drawback... well, it is pink-ish water. And the surprising fact is that this pink colouring establishes over time independent from adding fertilisers: it seems that plants are eating Fe(3+) and the remaining free EDDHA anions are just chelating Iron from either insoluble forms or from photodestructed Fe-DTPA producing more and more FeEDDHA in the water column (well, it is just my guess though).
I'm not extremely annoyed by this colouring counting that otherwise this mix works perfect, but I would appreciate any ideas about how to improve or 'fix' this mix :)
 
As far as I'm aware it's the FeEDDHA that causes the pink tinge, if you want to get rid of it you will need to stop replace it with DTPA, if you dose when you have a ph less than 7.0 you should be ok.
 
The problem with DTPA was that it disappeared from the sollution somehow. I don't know why, but after 1.5 months there was no iron in my mix (and there was a percipitate in the bottle). Mixing TEC-SF with a very small fraction of FeEDDHA (also from Solufeed) has fixed the problem - there is Iron and there is no percipitate now. But it seems that the side effect of mixing chelates is that free EDDHA ligands steal iron from other chelates and (probably) insoluble compounds. So if I could fix DTPA stability issue I would probably remove EDDHA from my mix (well, but the final result is basically replacement of pink with lime colouring in a tank).
 
What colour is the mix in the bottle?
It was initially light green to brownish, like this:
2021-08-21 21.33.13.jpg
After time, the colouration has turned towards being more and more brown.
Adding EDDHA to the mix apparently has switched colour to dark pink masking TEC-SF colours.
 
Well, after some thinking I have one idea but please correct me if I'm wrong. Probably the culprit was ascorbic acid - it is a reducing agent so it might have restored Fe(3+) to Fe(2+) making DTPA chelate less stable. Do you think it is possible?
 
I think Darrel might be the fellow to answer that question!
Seems that you might have stumbled on something there.....try making a mix up with out the Ascorbic Acid and with distilled water!
 
The first one was that due to high level of TE my normal dosing of 0.5ppm of Fe per week was a bit high for some plants (e.g. I've lost my Toninas).

1634378466306.png

1634378531499.png

The differences in TE (Trace Elements) compared to APFUK Trace has increases of 7%Mn, 33%Zn and a decrease of 14%B. which I felt was acceptable considering to actual small amounts being dosed, I sure @dw1305 will give his input.

there was some insoluble remain in the bottle of micro and the iron test has shown
How much of the trace mix was you adding to the dosing bottle? It was hard for use to find the actual solubilities of most trace elements and based them on what we could find and decided a solubility limit of 75g per Litre should be fine. Your feedback would be helpful as we could decrease the solubility limit in the IFC Fert Calculator which may help others.

I have decided to change micro by adding like 0.3ppm Fe on this mix + 0.1ppm Fe on FeEDDHA (also from Solufeed). This mix works just perfect for the plants and it stopped all issues with melting/chlorosis:
:thumbup:
But there is one drawback... well, it is pink-ish water.
Yes, I had my tank very pink at one stage, what I did was to decease the Fe EDDHA dose until I could only just see the slightest of pink tinges. I felt at that level the plants must be getting enough.

How much ascorbic acid was you adding per litre? you mix may just need a little more - I tend to add more than the recommend dose as weighing small amounts can be tricky and a little extra will make very little to no difference once it lands in the tank
 
The differences in TE (Trace Elements) compared to APFUK Trace has increases of 7%Mn, 33%Zn and a decrease of 14%B. which I felt was acceptable considering to actual small amounts being dosed, I sure @dw1305 will give his input.
TEC-SF is a different beast, it has Fe chelated by DTPA and different amount of traces:

Mg - 5ppm
Fe - 0.5ppm (DTPA)
Mn - 0.21ppm (EDTA)
B - 0.03ppm
Zn - 0.15 (EDTA)
Cu - 0.018 (EDTA)
Mo - 0.013
How much of the trace mix was you adding to the dosing bottle? It was hard for use to find the actual solubilities of most trace elements and based them on what we could find and decided a solubility limit of 75g per Litre should be fine. Your feedback would be helpful as we could decrease the solubility limit in the IFC Fert Calculator which may help others.
It was around 60g per litre.
Yes, I had my tank very pink at one stage, what I did was to decease the Fe EDDHA dose until I could only just see the slightest of pink tinges. I felt at that level the plants must be getting enough.
The interesting stuff is that pink colour is developing over time. So I think there is either extra EDDHA (unbound to Fe) or there is another effect where free ligands steal Fe from other forms.
How much ascorbic acid was you adding per litre? you mix may just need a little more - I tend to add more than the recommend dose as weighing small amounts can be tricky and a little extra will make very little to no difference once it lands in the tank
I've added 1g per Litre. Ferrous DTPA and ferrous EDTA are much less stable than Ferric ones, according to the following paper the stability constants for EDTA/DTPA are 14/16 for Fe(2+) and 25/28 for Fe(3+) respectively. If ascorbic acid can indeed reduce Fe(3+) in EDTA/DTPA than it is definitely better not to add it to the sollution.
 
TEC-SF is a different beast
Sorry my mistake :oops:, I selected the wrong one.

1634456730920.png

1634456773556.png

Good to see both are figures match for Solufeed TEC-ST. As you correctly pointed out it has double the amount of Mn and Zn and half the amount of B

It was around 60g per litre.
So getting close to 75g/L
The interesting stuff is that pink colour is developing over time.
I think mine did as well, I just reduced the Fe EDDHA dose a bit more
I've added 1g per Litre. Ferrous DTPA and ferrous EDTA are much less stable than Ferric ones, according to the following paper the stability constants for EDTA/DTPA are 14/16 for Fe(2+) and 25/28 for Fe(3+) respectively. If ascorbic acid can indeed reduce Fe(3+) in EDTA/DTPA than it is definitely better not to add it to the sollution.

Interesting, we could do with a little input from @X3NiTH me thinks ;)
 
I would redo the mix using 0ppm TDS RO/DI if you can to discount any compounds in the water that have a greater affinity for chelation than iron such as calcium, this would reduce the likelihood of the chelate swapping out the iron leaving it free to precipitate out or rechelate with Ascorbic acid and then reacting and dropping out.

I would also only use as a maximum enough Ascorbic acid to cause the greatest pH drop for the least amount of compound added, this is approximately 0.5g of Ascorbic to 1L of receiving water resulting in a pH of 3.25 (you could use less and target a higher pH), trying to reach a much lower pH requires a magnitude more of the compound to reach a further pH drop. I will assume any excess Ascorbic acid in the solution beyond the maximum pH moderation required is joining in the chelation game, if there are other compounds in the water other than iron that the desired chelate may swap out for then this leaves the iron free to chelate or react with the excess Ascorbic acid or drop out of solution.

If Ascorbic acid causes too much longevity problems for certain compounds needing acid moderation in these solutions then it might be best to swap to another acid that doesn’t have chelatory properties like Muriatic or Sulphuric acid.

Temperature may also be a factor for reactions so it would probably be best to refrigerate the solution after mixing, I refrigerate my mix and it retains its green colour but the amount decanted into the dosing bag can see fluctuating temperatures and this summer it spent a lot of time above 25c, the mixture does brown somewhat but doesn’t precipitate, the browning I will assume is a consequence of not being stored in light tight conditions as its wrapped in opaque plastic where light may sneak in and around the folds exposing the mixture to possible photoreduction.

I have never tested for the levels of iron after a few months in the bag, usually the first thing I notice if there is a problem with micro dosing is that Buce will start to throw a fit, this is either because the dosing lines have clogged with mold that has made it into the dosing line or the solution has run out. After clearing the lines out when there is a blockage and resumption of dosing with the remainder of the solution left in the bag then the plants go back to normal with ceasing of leaf shed to the retention of leaves and resumption of new tissue growth.

I haven’t used EDDHA so I can’t comment on the reactions but from what has been described so far there is every chance that it may be re chelating iron and increasing colour tint over time, I tried looking for the spectra of other EDDHA complexes such as with Calcium and Magnesium to discount these elements but I couldn’t find anything in the short time that I looked.

:)
 
Well, I have mixed a fresh portion without ascorbic acid and whithout FeEDDHA. And the colour of the sollution is now brown not green from the very beginning. Apparently there is no percipitation so far in the bottle.
 
As long as there is no precipitation and you get a positive result from an Iron test then this solution is your baseline, it might be worth taking a note of the pH of this solution, if it remains stable then I would add the FeEDDHA and note for any change in pH or stability of the mixture (colour change, precipitation, iron content measured different to that calculated). If the pH of the mix remains low enough for the mixture to remain stable long term then you can continue to skip the acid addition entirely for future mixes as long as you can replicate the same conditions for this so far working recipe.

:)
 

@X3NiTH me and Darrel we were just talking about the use of HCL to reduce the PH of the solution, we also discussed about the use of Citric Acid as well. H2SO4 was also on the table as well. there are several other PH reducing chemicals out there, we usually use Asrobic acid or Vinegar. Vinegar is probably the cheapest and quite effective alternative if you want to play it safer.


@Vsevolod Stakhov is probably experiencing whatever I experience from time to time while using Asrobic acid. I think i described this issues in one of the thread. my only guess is that the more Asrobic acid we add, it break down the Chelate and possibly precipitate the Iron and other elements, this occurred even while using a pure Distilled water to make the solution.


i hope @@Vsevolod Stakhov posts more update on this topic and his finding. EDDHA is fine to use as well, I use to mix this with DTPA Fe, around 0.02 ppm EDDHA per dose. this shouldn't tint your water and works quite well if you still want to continue to use it, but DTPA Fe alone should be fine as well.

our dear Friend Marcel strongly suggested using DTPA and I completely agree with him, here is the link to that: DTPA or HEEDTA - which is better for plants ?
 
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H2SO4 was also on the table as well
And I've added ascorbic acid to ensure that the final PH is low enough and to 'eat' the remaining bicarbonates.
Nice plants.

I use KHSO4 to reduce pH. It acts in solution as a mixture of potassium sulphate and sulphuric acid. It is corrosive but is easy to handle. I just add a small crystal to the stock bottle of EDTA Fe and Trace mix. It lasts for months. The bottle (5 litres) is painted mat black and kept in a dark cupboard. The solution is always pale green/yellow, just like a urine sample on a good day.

It is important to use Distilled or RO or Rain Water. Group II ions, Ca & Mg, unless chelated, will replace Iron and other Transition Metals from chelation.

Not concerned about stability in the display tank, I run a soft water setup and traces are dosed alternate days as per EI methodology.
 
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