# Does Ferrous Gluconate Cause A Water Surface Film?



## jaypeecee (15 Sep 2019)

Hi Folks,

Whenever I use Seachem Flourish 'Comprehensive' or Flourish Iron, an oily film develops on the surface of the water. Both these products contain ferrous gluconate. Is it reasonable to conclude that ferrous gluconate may be causing the surface film that I am seeing?

I will add that the surface film does break down (by bacterial action?) within a day or so but I would prefer that it wasn't there. Firstly, it is obviously unsightly and, secondly, it interferes with O2/CO2 gas exchange at the water surface.

Any comments appreciated.

JPC


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## jaypeecee (15 Sep 2019)

Hi Folks,

Further to my question above, I have been digging around to see if I could find an answer to this question. It may be a bit of a stab in the dark but I have discovered that there are such things as iron bacteria, one of which is called Leptothrix discophora. Apparently, these naturally-occurring bacteria feed on ferrous iron secreting proteins and carbohydrates in the process. The resulting biofilm sticks to the surface of the water. I now need an expert to tell me that my hypothesis is way off the mark.

JPC


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## jaypeecee (18 Sep 2019)

Hi Folks,

Does anyone else use Seachem Flourish 'Comprehensive' and/or Flourish Iron? If so, do you get an oily film that forms on the water surface?

JPC


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## oscarlloydjohn (18 Sep 2019)

I'm not sure about Ferrous Gluconate causing the surface scum, however from what I have read I understand it involves biochemical oxygen demand.


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## jaypeecee (24 Sep 2019)

jaypeecee said:


> Hi Folks,
> 
> Does anyone else use Seachem Flourish 'Comprehensive' and/or Flourish Iron? If so, do you get an oily film that forms on the water surface?
> 
> JPC



Am I really the only person on UKAPS that uses the above products?

JPC


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## sparkyweasel (24 Sep 2019)

Quite possibly; a lot of people mix their own fertz instead of buying expensive products that are mostly water, which is expensive to ship.


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## jaypeecee (25 Sep 2019)

sparkyweasel said:


> Quite possibly; a lot of people mix their own fertz instead of buying expensive products that are mostly water, which is expensive to ship.



Hi sparky,

Thanks for your reply - I was starting to think that I had the forum equivalent of bad breath or something (due to the lack of replies)!

I am aware that a lot of people mix their own fertilizers but I thought there may be some aquarists that used commercial products. You raise a good point about shipment costs as Seachem products have to be shipped from the US of A. And, as you say, a large proportion of ferts will probably be water. Shame they don't ship the dry fert mixture instead. But, I guess, it's not difficult to buy the individual ferts instead.

JPC


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## jaypeecee (24 Oct 2019)

jaypeecee said:


> It may be a bit of a stab in the dark but I have discovered that there are such things as iron bacteria, one of which is called Leptothrix discophora. Apparently, these naturally-occurring bacteria feed on ferrous iron secreting proteins and carbohydrates in the process. The resulting biofilm sticks to the surface of the water. I now need an expert to tell me that my hypothesis is way off the mark.



Hi Folks,

I realize that many things can cause a surface film. But, if iron bacteria are known to cause surface films and other people are adding ferrous iron without having problems, then does that mean that I'm the only person with this type of bacteria in my tank? Seems very unlikely. I guess this points to the fact that the reason for the surface film lies elsewhere.

JPC


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## jaypeecee (26 Oct 2019)

jaypeecee said:


> I realize that many things can cause a surface film. But, if iron bacteria are known to cause surface films and other people are adding ferrous iron without having problems, then does that mean that I'm the only person with this type of bacteria in my tank? Seems very unlikely. I guess this points to the fact that the reason for the surface film lies elsewhere.



Hi Folks,

Here on UKAPS, I found a link to an interesting report, which I have attached. The following sentence grabbed my attention:

"Iron bacteria growth is very dependent upon the pH level, occurring over a range of 5.5 to 8.2 with 6.5 being the optimum level".

My tank water hovers around pH = 6.5. 

JPC


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## sparkyweasel (26 Oct 2019)

I think pH6.5 is the optimum for many kinds of bacteria and other organic processes, so I wouldn't take that as confirmation of the source of your film. 
You said the film appears after you add your ferts, - could you try a different brand for a while and see if that stops it?


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## jaypeecee (26 Oct 2019)

sparkyweasel said:


> I think pH6.5 is the optimum for many kinds of bacteria and other organic processes, so I wouldn't take that as confirmation of the source of your film.
> You said the film appears after you add your ferts, - could you try a different brand for a while and see if that stops it?



Hi sparky,

Currently, my main fertilizer is TNC _Complete_, which contains 0.08% iron but, after a week, it has been depleted from the water column. Off hand, I don't know what form the iron takes in this TNC product. So, I then add one-third strength Flourish Iron. But, both these ferts appear to promote this unsightly film. The dilemma is that ferrous iron seems to be the preferred form for aquatic plants but that is the very form on which iron bacteria feed. It probably sounds as if I've conjured up the term 'iron bacteria'. But they do exist. Take a look at this:

https://www.aquasabi.com/aquascaping-wiki_filtration_getting-rid-of-surface-scum

JPC


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