# Solufeed TEC-SF usage experience



## Vsevolod Stakhov (15 Oct 2021)

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:







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


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## papa_c (15 Oct 2021)

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.


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## Vsevolod Stakhov (16 Oct 2021)

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).


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## GHNelson (16 Oct 2021)

What water did you use to make up the mix!


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## Vsevolod Stakhov (16 Oct 2021)

GHNelson said:


> What water did you use to make up the mix!


I've used RO water (10ppm on TDS meter). And I've added ascorbic acid to ensure that the final PH is low enough and to 'eat' the remaining bicarbonates.


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## GHNelson (16 Oct 2021)

What colour is the mix in the bottle?


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## Vsevolod Stakhov (16 Oct 2021)

GHNelson said:


> What colour is the mix in the bottle?


It was initially light green to brownish, like this:



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.


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## GHNelson (16 Oct 2021)

Yeah, I see what you mean!
Bit strange......


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## Vsevolod Stakhov (16 Oct 2021)

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?


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## GHNelson (16 Oct 2021)

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!


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## papa_c (16 Oct 2021)

Vsevolod Stakhov said:


> but after 1.5 months there was no iron in my mix (and there was a percipitate in the bottle



Gonna suggest the simple, why mix up such large quantities?  Make smaller batch say 3 weeks worth and you should be ok....


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## Zeus. (16 Oct 2021)

Vsevolod Stakhov said:


> 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 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.



Vsevolod Stakhov said:


> 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.



Vsevolod Stakhov said:


> 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:





Vsevolod Stakhov said:


> 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


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## Vsevolod Stakhov (16 Oct 2021)

Zeus. said:


> 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 - *0.21*ppm (EDTA)
B - 0.03ppm
Zn - *0.15* (EDTA)
Cu - 0.018 (EDTA)
Mo - 0.013


Zeus. said:


> 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.


Zeus. said:


> 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.


Zeus. said:


> 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.


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## Vsevolod Stakhov (16 Oct 2021)

papa_c said:


> Gonna suggest the simple, why mix up such large quantities


Yes, that's what I did in the first place  I'm just curious about the chemistry of the processes here.


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## Zeus. (17 Oct 2021)

Vsevolod Stakhov said:


> TEC-*SF* is a different beast


Sorry my mistake , I selected the wrong one.







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



Vsevolod Stakhov said:


> It was around 60g per litre.


So getting close to 75g/L


Vsevolod Stakhov said:


> 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


Vsevolod Stakhov said:


> 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


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## X3NiTH (17 Oct 2021)

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.


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## Vsevolod Stakhov (26 Oct 2021)

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.


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## X3NiTH (27 Oct 2021)

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.


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## Happi (11 Nov 2021)

*@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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## Oldguy (11 Nov 2021)

Happi said:


> H2SO4 was also on the table as well





Vsevolod Stakhov said:


> 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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## X3NiTH (12 Nov 2021)

Happi said:


> @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.



Fundamentally what is happening is that increased acid addition is changing the solution charge equilibrium toward an increase in protonation, the solution therefore is out of charge balance and as such there will be reactions between the elements within the solution to bring it back into balance even when all compounds are below their solubility threshold. More complex acids like Ascorbic and Acetic introduce carbon into the equation which will form part of reaction products to balance the charge, this would increase the chances of carbonate compound formations which can be fairly insoluble, a simple acid like HCl reduces the complexity of the charge balance equation and if compounds are formed they will be more likely chlorides which are very soluble so the chances for precipitative effects are much more reduced.

You can calculate the charge balance for a pH moderated solution of chosen compound molar concentration beforehand to reduce the likelihood of precipative effects but it becomes a very Complex Equilibrium Equation as you add more compounds in differing molar concentration.

The document below is an exceptional read and has all the equations within to calculate the above and so much more!

W. M. White Geochemistry Chapter 6: Aquatic Chemistry


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## X3NiTH (12 Nov 2021)

Oldguy said:


> 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.



Here is the Affinity graph for EDTA.


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## dw1305 (12 Nov 2021)

Hi all, 


X3NiTH said:


> The document below is an exceptional read and has all the equations within to calculate the above and so much more!
> 
> W. M. White Geochemistry Chapter 6: Aquatic Chemistry


That is very useful,  thank you. 

cheers Darrel


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## Happi (12 Nov 2021)

Bit off topic but I have a solution that is made out of CaNO3, Mgno3, Kno3, urea, kcl, Traces EDTA based, Fe EDTA, Fe DTPA, Fe EDDHA.

No PO4 added to this, it's also free of Sulphate, it was made in May 25th, 2020 and stored in the garage where it has seen both hot and cold days. The solution is quite stable without any prectipation, it's wine color. I believe the EDDHA and DTPA is doing the major work here.

Note: the Bottle looks dirty with dust, debris etc attached to it on the outside, don't assume that as a prectipations.


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## Vsevolod Stakhov (12 Nov 2021)

X3NiTH said:


> Here is the Affinity graph for EDTA.


Well, Ca/Mg EDTA chelates are stable merely in alkaline PH (that's why our GH test has to establish alkaline conditions first). I think the point was that bicarbonates of alkaline metals can set the overall alkaline reaction of a water sollution (as they are the salts of a weak acid and a strong hydroxide). So if you want to add Fe or other heavy metal salt to be chelated, you need to ensure that the PH is suitable for that. For example, addition  FeSO4 to 4NaEDTA sollution will just produce perciptation of the Fe(OH)2, whilst addition 4NaEDTA to FeSO4 will produce FeEDTA- as expected (because FeSO4 is an acidic salt that has PH~3).

I've also investigated my initial situation with ascorbic acid. The only hypothesis I have is indeed that there was too low PH in my sollution. EDTA and DTPA as acids are insoluble in water. And we also know that Solufeed chelates do not have Na cations in the external sphere but NH4 ones. NH4+ is a very weak alkali comparing to Na+, so presumably the PH of the sollution was too low to move EDTA/DTPA to unsoluble state. I don't know what happens to the internal sphere (where Fe ion is placed) during this process, I'm afraid. However, removing acorbic acid seems to slow down this process slightly.

The colour is still changing from bright green to yellow/brown (this might just be related to Fe2+ -> Fe3+ oxidation). And I still see some perciptation unfortunately. On the other hand, JBL tests still shows that there is enough iron in soluble state in both tank water and in the fertiliser.


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## Oldguy (13 Nov 2021)

Vsevolod Stakhov said:


> Solufeed chelates do not have Na cations in the external sphere but NH4 ones.


EDTA does not contain NH4 but has amine groups that are covalently bonded to the resultant ligand that partially or fully encapsulates the central metal ion that has been chelated. These amine groups are not ionic and are stable even when the central metal ion is removed or replaced. 
The Na or K ions (dependent on formulation) just balance the resultating net ionic charge of the chelated complex.


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## Vsevolod Stakhov (13 Nov 2021)

Oldguy said:


> The Na or K ions (dependent on formulation) just balance the resultating net ionic charge of the chelated complex.


I'm talking about the external sphere of a chelate. It has either H+ or Na/K/NH4 cations or some combinations (like 2Na2H EDTA). As far as I know, Solufeed uses NH4 instead of Na to balance the external sphere, but I might be wrong here and there are K+ cations there (but definitely not Na, as it is Sodium free mix).


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## X3NiTH (13 Nov 2021)

The Solufeed mentioned above isn’t using Sodium EDTA, it’s either Diammonium EDTA or Potassium EDTA depending on the Ion to be chelated, blended trace mix will be using a combination of them both. 

This is what PubChem has to say about Edetate Diammonium and Edetate Dipotassium.

Here’s DOW chemicals Technical Specs for their Diammonium EDTA, Tech Specs for their Potassium EDTA are not available.








I’ll bet that Solufeeds formulation will be identical.

Take note of the pH of solubility and the fact that Ammonium is the Protonated form of Ammonia and that if this is used in ranges outside it’s solubility it could be problematical in above neutral pH conditions (?Ammonia Toxicity) if overdosed accidentally into an aquarium, the fear may be unfounded but I would still be aware.


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## Vsevolod Stakhov (13 Nov 2021)

Vsevolod Stakhov said:


> As far as I know, Solufeed uses NH4 instead of Na


Well, it seems this is not correct for some trace elements. According to another mix they use the following chelates:
CuNH4EDTA
FeKEDTA
Mn2KEDTA
Zn2KEDTA

However, for DTPA they sell the only one sodium free chelate: ferric ammonium DTPA. So my assumption that the external sphere ions are (mostly) NH4+ seems to be correct after all.


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## X3NiTH (13 Nov 2021)

Vsevolod Stakhov said:


> So my assumption that the external sphere ions are (mostly) NH4+ seems to be correct after all.



Yup!


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## Happi (13 Nov 2021)

I believe X3NiTH and Oldguy is referring to this, most Chelate will have the N in the amine groups which is actually utilized by the plants quite well. EDTA also contain Na while DTPA doesn't, some Hydroponic people don't use Fe EDTA but rather prefer Fe DTPA because Fe EDTA is toxic and is used as Herbicides. Fe HEDTA used for killing weed:​Using iron-based herbicides for alternative weed control. - My Green Montgomery​


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## Happi (13 Nov 2021)

Vsevolod Stakhov said:


> Well, it seems this is not correct for some trace elements. According to another mix they use the following chelates:
> CuNH4EDTA
> FeKEDTA
> Mn2KEDTA
> ...


in theory these would be better for our aquatic plant with addition of NH4 and no Sodium Compared to some Chelate such as Sodium based EDTA. send some to USA for me


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## Oldguy (14 Nov 2021)

Vsevolod Stakhov said:


> NH4+ seems to be correct after all.


My stock of Iron EDTA has sodium cations to 'balance' the anion EDTA complex.

Did not know that ammonium cations were now being used but were aware that potassium cations were available.

Bought my stock over 15yrs ago when its main application was as a folia feed for top fruit, especially the one with trace elements combined in the mix. The later was not then available in the small kg bags.

Like this forum always learning new things and being updated on new products.


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## Vsevolod Stakhov (15 Nov 2021)

Happi said:


> in theory these would be better for our aquatic plant with addition of NH4 and no Sodium


Yes, but even on the EI Fe addition as 0.5ppm per week, the amount of counter-ions is quite negligible, for either Sodium or NH4/K+ (less than 0.5ppm due to molar weight). 
I have measured the PH of the browned sollution and it seems to be around 7-8 (harder to say more precisely as it is coloured itself, so I have to use either test strips or try to guess using liquid tests). The Fe there is still solluble and detectable but I would definitely prefer to make a fresh sollution more frequently, as it seems to be less stable than EDDHA added mix. On the other hand, I like that there is no more pink colouring in the water, and the plants look good after all:


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## Vsevolod Stakhov (26 Aug 2022)

I have recently observed a strange effect after adding this feriliser that I personally could not explain at all. So I add Solufeed TEC-SF to my 3 tanks to level of 0.1ppm Fe 3 times per week (combining with FeDTPA 0.1 * 2 times per week). However, last time I've added this combination to my malawi tank, all fishes were struggled to breath showing clear signs of low oxygen: gasping air, frequent breathing etc. I've immediately increased aeration and changed around 10% of water from tap, so it was clearly a lack of dissolved oxygen somehow.

But other two softwater (KH=1..4) tanks were totally fine, it was only cichlids tank that suffered. It is different as it uses pure tap water with KH=12 and GH=18 (110ppm Ca). I'm also observing that the water during water changes has somehow turquoise or aquamarine colour . This colour is also quite unique for this tank, and it is not caused by algae or something - the water is crystal clear. Softwater tanks' water does not have such a colour, just in case.

So I really cannot answer a question about how an addition of the micro-elements could cause oxygen depletion. The chelates are not "easy" organic, such as gluconate, so it might be something else (however, even most simple organic would not cause that fast oxygen depletion). I also cannot explain the colour of the water at all.

Of course, that could be a coincidence (and it's likely so), but probably someone has any thoughts on that before I try to dose that fertiliser one more time in that tank.


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