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Surface Film

George Farmer said:
What do you think is causing it, Mark?

The scum is pure white and has a waxy feel to it

Thats exactly like the film was on my surface,i did notice it got better when i stopped dosing easy carbo for a week,but as an experiment i started to dose 1 ml a day and hey presto it was back in 2 days just as bad,now i am not saying that its mainly caused by easy carbo, but i think it may be an excess of co2 :?: ,since i have stopped the easy carbo its no where near as bad so really i am non the wiser as i have upped my co2,

regards john
George Farmer said:
What do you think is causing it, Mark?

in all honesty, i'm not sure.

My observation's tell me, when more co2 is added it can get worse (sorry Clive) but it does.

I believe, (without scientific back up) it's instability with biological contents of the tank, or lack of it. I get it on start up, to about 7 or 8 weeks in backing my belief up. Then, as things 'settle' or stabilize, it goes... a bit like diatoms.
here you go.

The old prairie lands a year ago. The reason i ripped it down.

chronic algae...


I got fed up with this. so left it to see what happened...


surface scum builds. leaving it deprives the tank of oxygen i reckon.



Now fast forward a year, with better knowledge, maintenance and things are different. I still get it slightly, but skim it off everyday, it'll go in time.

Notice the lighting height to.


Mark that third shot is exactly like the film i get :crazy: ,

i also get the '3rd' shot scum in my nano as well. I'm not injecting C02, just dosing easycarbo, i also dose profito a couple of times a week. The light is low. I also had this in an old tank, now the only thing i can see/put a link to is that i used/use zeolite in both tanks.The nano is heavliy planted with riccia and its really healthy. It doesn't bother me as i can just jug it off every couple of days.
Hi Mark,
I think you might be mixing up cause and effect. As mentioned before there is a relationship between the metabolic rate and the production of organic waste. If you feed the plants more CO2 then they will eject more waste products. So it's not surprising that more fats, oils and carbohydrates are ejected with increase metabolism due to increased consumption of CO2. The next step though is that with an increase in CO2 consumption there is a demand for more nutrients. The nutrient loading must match the CO2 loading. If the higher CO2 consumption is not matched by higher nutrient consumption, then the waste ejection is higher than normal.

CO2 metabolism is a much more complicated issue than nutrient consumption because of the Rubisco transport mechanism. You can lower the CO2, keep the same lighting and then you can observe an increase in the scum. If the CO2 was lowered only a small amount the scum may last only a few weeks as the plant adapts to the lowered CO2 level. If the new CO2 level is within the tolerance range for that lighting level then the plant can adapt. If the Lower CO2 level is too drastic for the lighting level then the plants continue to leach waste products into the water column. This then becomes a chronic issue and can lead to other CO2 deficiency symptoms.

If lighting level and nutrient levels are held constant, but if CO2 is increased, then this could lead to a demand for higher nutrient uptake. If this is not met then the excess ejection is caused by nutrient deficiency. Again, depending on how much more CO2 is being consumed, this determines the severity of the nutrient deficiency. If the increase in CO2 is mild to middling, then after a few weeks the plant has the ability to adapt by becoming more efficient at nutrient uptake. If the CO2 increase is significant then this may fall outside the range of the adaptability.

So it's very difficult to predict exactly how many ppm of this or that will result in excessive or normal ejection because of the range of adaptability and the degree of movement in all the associated variables. Not only are the environmental variables changing, but the plant themselves are changing. They increase in mass by growing, or decrease in mass by trimming or by loss of weight due to deficiency. So the same conditions may be present in two tanks but the symptoms may only appear in one tank due to lower bio-mass in one tank versus the other. Their energy reserves may be high or low which affects the speed and duration at which the symptoms appear or disappear. In order to get to the root of the problem one has to be able to control all variables in the equation, and that simply doesn't happen. People become impatient because we all want a quick fix. And that's why we draw these premature conclusions.

I use tons of CO2 and I don't have any of these issues. I can add more CO2 and the only thing that happens is more health, clearer water and more pearling. In my case I don't have to make any adjustments to nutrient levels because they are already unlimited.

This problem also has been reported in non-CO2 tanks. So the conclusion that this is caused strictly by CO2 can't be true unilaterally. This is an illusion and we simply haven't figured out the magicians trick.

In this shot I turned the filters off for a few hours to see how much oily film was actually present. There was very little, although you could see a thin film.

So generally, it really depends on where you are in terms of plant health and nutrition, not just "did I add more CO2", even though it might appear so at face value. Health and nutrition are always going to be linked to lighting intensity, flow/distribution, nutrient levels, bio-mass and so forth.

Surface film does not always deprive the tank of Oxygen. The film block gas transport across the air/water interface. Therefore, if the plants are producing Oxygen during the photoperiod, then less oxygen escapes to atmosphere. If the Oxygen level falls below atmospheric levels during the night then yes, the film does lower Oxygen ingress into the tank. The same goes for CO2.

It wouldn't be surprising at all that algal blooms in the tank are either accompanied by, or preceded by surface scum, because these are both health and nutrition related. In fact, typically one gets the film and then the algae. The film is a harbinger of doom because it's telling you that you have health issues.

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I had the same film and I attributed it to crypts, as soon as I removed the crypts the film went, never noticed it with any other plant but crypts before or since though I see that I must have lowered the co2/nutrient demand by removing them and not seen the true reason for the film. I think it might be a natural part of start up to an extent, plants will be melting/shedding old leaves etc but I could be wrong?
Hi all,
I think the surface scum is mainly "biofilm" as well. My thoughts are that the plants are naturally quite "leaky" and produce lipids, carbohydrates etc. The scum is formed when these compounds build up, and are colonised by bacteria etc. It actually has a scientific name, the "neuston".

This is from Brett the Skeptical Aquarist, who is a much better writer than I am.
In fairly still ("lentic") waters, surface tension creates a stable environment for organisms and offers the best access to carbon dioxide and oxygen in the air. The density of living cells on the surface may be ten to a hundred times what it is in the water layers just beneath the surface slick. Many bacterial strains in this biologically-enriched surface layer carry photosynthetic pigments, though you might not notice cyanobacteria, for example, until they stain your paper towel blue-green. There are also true algae, diatoms, fungi and single-celled protozoans in these organically-enriched microlayers.
A surface skimmer or daily paper towel wipe or increased flow or increased water changes will remove it, and if you combine low-tech and water changes you don't get it at all.

Another possibility is that the aquarium is open topped? in which case the film may also have oil or wax droplets from cooking, furniture cleaner etc or even bio-particulates from the terpenes and propellants in aerosols.

cheers Darrel
Funny that you mention crypts as I do have crypts in my tanks. However this has only stared happening when the weather has gotten colder.

I notice that my tubs of moss by the window sill also have a film on top of the water. Weird. I now do daily water changes with my main tank water to ward this off.

Sadly my nano is open toppped and low tech. Lighting is around 6 hrs a day and I have a hob filter.
This has been the bane of my tanks life too at the moment. Both Garuf's and migt's findings with crypts are true to me also. I believe my problem is still a lack of flow delivering CO2 so I'm going to try ditch the crypts as a solution and make it a completely moss tank to reduce CO2/nutrient demand. Interesting post.

I don't have a chemistry degree but I have to wonder what adding EI ferts + high levels of co2 to a tank do to the water chemistry.

I was once told that the scum on top of the bath water was mostly calcium carbonate.

How do all these salts and co2 interact in the water column before we consider the substances released by the plants if they're in suboptimal health?

My water has loads of calcium in it. If I add lots of co2 will they interact?
I've had surface film/scum with EI/High Tec and non-EI/Low Tec, so I can't link the two together.
Noticed that if there is very little surface movement this surface scum rears it ugly head.
That's in both cases high tec and low tec.
If you use a air stone at night when the Co2 has switched off I bet you don't get this film on the surface in the morning.
NeilW said:
This has been the bane of my tanks life too at the moment. Both Garuf's and migt's findings with crypts are true to me also.
Well, I mean if you have a big plant and it's suffering then this plant will contribute to the problem, but don't blame it on the plant. Fix the real problem. I've had loads of crypts and don't have this problem, so it can't be due to crypts.
NeilW said:
I believe my problem is still a lack of flow delivering CO2 so I'm going to try ditch the crypts as a solution and make it a completely moss tank to reduce CO2/nutrient demand.
OK, so have you considered the benefits to the tank of healthy crypts and what it is that you're giving up by ditching them? How about lowering the light intensity? How about experimenting with the nutrient levels?
tyrophagus said:
I don't have a chemistry degree but I have to wonder what adding EI ferts + high levels of co2 to a tank do to the water chemistry.
It does lots of things but it only indirectly affects surface scum.
tyrophagus said:
I was once told that the scum on top of the bath water was mostly calcium carbonate.
Calcium Carbonate is the substance in your tap water that causes the water to be both high in Carbonate hardness (KH) as well as General Hardness (GH) from the Calcium. Calcium Carbonate is easily dissolved by acids, and in nature, dissolved CO2 in groundwater generates Carbonic acid which then dissolves the CaCO3 and that's how it gets into your tap water supply. Calcium Carbonate is otherwise known as Limestone, or Chalk. There are no relevant interactions of the nutrient salts with CaCO3, however one trick when taking a bath is to add Epsom Salts (MgSO4) to the bath water which helps to prevent soap scum. High CO2 concentration in the aquarium water means high Carbonic acid content which dissolves the CaCO3 and keeps it in solution. You're barking up the wrong tree if you think EI is responsible for surface scum, which is made of oils and other carbon products.

You see these EI fed crypts? The tallest lances are 2 feet long. They are shown in the peak of health as you can see by the sheen of the leaf surface. There is no algae and the water's surface is immaculate. Linking EI to surface scum is like blaming algae on nutrients.

Have you ever seen that TV series Kung Fu? The one with David Carradine? Remember when he first entered the Temple and had to snatch the pebble from the master's hand? Well guess what? This is your pebble. When you can grow crypts that look like this then you automatically won't have surface scum. If you've got surface scum you must have the discipline to blame your own poor technique. Just because you added CO2 it doesn't mean that you added enough. Just because you added more flow it doesn't mean that you added enough. Just because you added nutrients it doesn't mean that you added enough.
Always start with lighting as suspect number 1.

I find a quick scoot over with a small aquarium net clears it quick enough and is less messy than paper towels.

I actually notice that from the water change day when the scum is gone, then it builds up over the week, that by the end of the week the fish can begin to hang around the top of the water more often so I can only assume it is affecting either oxygen getting in to the water and/or CO2 getting out.
Does the "fats" produced when you move your finger the film do any harm to the fishes?

Reason I asked is I would blow at the floating plants if they were to get caught up in the corners and when doing so a lovely while substance from the film falls into the tank.
Well these products rot, attract bacteria and may ultimately result in ammonia production depending on content, so while they may not directly be a hazard they are organic waste which is not good generally.

Plant cells are typically constructed of a membrane called a "bi-lipid layer" also called "phospholipid" layer. This is a compound consisting of two fatty acid chains linked to a glycerol molecule (glycerol is similar to glycerin, that sweet viscous clear liquid.)


In this photo you can see where the "bi" name comes from. The white "head" is the glycerol and it's attached to two orange "tails". These tails are the lipids. The membrane consists of two sheets of these molecules inverted so that the fatty acid or lipid tails touch, but the heads are on the far side. In this photo the lower white heads face the inside of the cell and the upper white heads face the outside of the cell.

The white glycerol+phosphate heads are polar. That means they have an varying electric charge across the shape of the head. Phosphate is highly polar and helps this function of the head. Water is also a polar molecule. In fact it's one of, if not THE most highly polarized liquid on the planet. Waters polarity is one of the things that makes it the most amazing liquid. This means that the negatively charged part of a water molecule is attracted to the positively charged side of the white head. This polar attraction is what makes things soluble in water. Things that are soluble in water are called "hydrophilic" i.e. water-loving.

The fatty acid orange tails are non-polar. Fats, lipids and oil are all non-polar. They have no attraction to water. That's why oil and water do not mix. That's why oil, being lighter than water floats. Non-polar substances that are not attracted to water are called "hydrophobic" i.e afraid of water.

The plant cell membranes are therefore both hydrophilic and hydrophobic at the same time. This property allows the cells to be selective about which chemicals can enter or leave the cell. For example, the white heads mix with water, and so objects that are dissolved in water can be carried to, and attracted to the heads but the water cannot penetrate the central lipid layer because it's basically made of oil, which rejects the water and therefore rejects any other polar substance dissolved in the water.

In order to select specific chemicals the phospholipid layer is studded with "channels" which are just various proteins which are designed to have special attraction to specific chemicals. When those chemicals are dissolved in the water and touch their favorite channel they are pulled into the channel and avoid the lipid tails by traveling through the protein as if they were traveling through a tunnel. Here is a schematic of channels studded across and through a bi-lipid layer:

The fatty acid tails and the proteins studding the cell membrane are the source of polyunsaturated fats. This is exactly why eating vegetables and leafy plants are good for you. This is the source of vegetable oil. Plants that die and become fossilized under great pressures underground have their lipids converted to a hydrocarbon form we call crude oil. Plants are the source of your petrol. This is why petroleum is called fossil fuel.

When the plant is under nutrient and/or CO2 stress their cells rupture. What you then see on the surface are the lipid tails and fatty acid products destroyed and spewed out. The hydrophobic nature of the tails send them to the surface. This is a combination of pre-petroleum and glycerine products floating on the surface, telling you that the plants are under duress.

Paper towels, fish nets and skimmers do not solve the basic problem of environmental stress. The proper path is to solve the malnutrition or to reduce the lighting to lower the nutrient/CO2 uptake demand.

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