Chapter 26. Scums and slimes of the aquarium. No.1 Surface scums.

If anything good has come from the previous 314 weeks of maintaining a largely cyanobacteria infested aquarium, it is that it has encouraged a keen interest in microscopy in me. Although I can take samples into work and use the microscopes there, I decided to treat myself and bought my own.

The main advantages are that I can examine samples fresh from the aquariums and much more thoroughly than at work. But before I reveal anything about comparing my cyano infested and cyano free aquaria, I wanted to answer some questions I've long had about the various scums and slimes I see at different times and in different places in the tanks.

I began with the white foamy surface scum that occasionally forms behind the canister filter in my heated cyano infested tank. Here the scum has been forming for two weeks.

A child of still waters-white foamy surface scum.

My question was, is it of biological origin?  This video at x100 magnification suggests that the scum supports abundant life. I was surprised by all the activity, I have never seen such a concentration of ciliated protozoa in any other part of the tank. But the most interesting thing for me was that the ciliates were obviously swimming within a membranous structure. In the video this structure has become folded in upon itself, presumably when I scooped some of the scum up with a cocktail stick and put it on a microscope slide. But what is it composed of?

Aquarium foamy surface scum at x400 magnification

A network of filaments of varying thicknesses was revealed at x400 magnification but the network doesn't look dense enough to appear as a continuous "membrane" at x100 mag in the video. My guess is that the filaments are growing alongside the "membrane". The filaments I think explain why this is a foamy surface scum as filaments are excellent at trapping air bubbles. The thick filaments are 5 to 6.5 micrometers wide and branched, I think they're almost certainly fungal.

Aquarium foamy scum at x1000 magnification. Fungal hyphae 5 to 6.5 microns wide.

So, I had discovered a strange membranous structure associated with a fungal matt and abundant ciliated protozoa, but what is the food source for this community? This question led me to start thinking about my aquarium surface. I agitate the surface of my aquarium with bubbles from a powerhead and venturi valve because if I don't an oily surface scum develops.

One week old aquarium oily surface scum broken up during a water change.

The above photo was taken after a water change in W313. Before the water change I had closed the venturi valve for a week to allow the scum to form. The scum is fragmented due to to my activities during the water change. I always thought of this scum as oily because it floated on water and in a certain light refracted light in a similar way to petrol in a puddle (although not with the same intensity and range of colour). I wanted to examine the scum under the microscope in the least invasive way possible. I dipped a microscope slide into the tank and managed to scoop up some of the scum still floating on a bead of water. I then viewed at x100 magnification so I didn't have to use a cover slip and squash the sample.

Aquarium oily surface scum x100 with no cover slip. And they say it's difficult to see bacteria with standard light microscopy.

Obviously there are a great many small objects floating on the surface, and they appear to be aggregated into groups. They also seem to be a variety of colours, surely they couldn't be cyanobacteria?

Aquarium oily surface scum x100 zoomed digitally x12. For reasons I don't understand the cocci appear coloured and the bacilli don't .

Digitally zooming in reveals that the coloured aggregates are not isolated, they exist alongside darker rod shaped objects that are not visible without zoom. Interestingly the coloured objects seem to come as pairs or even groups of four. To discover their identity I had to use more powerful objective and so put a cover-slip on the sample.

Aquarium oily surface scum x1000 oil immersion, bright field. Bacilli and cocci.

The cover-slip doesn't seem to have had much effect, the sample surface is still populated by large numbers of objects of various shapes and sizes although they do appear to be more spaced out. The rods are less than one micrometer wide and can be seen singly and forming chains and there are thicker objects that seem to come in pairs or tetrads. The image is very much like the zoomed image above except that none of the objects appear coloured. I think they can only be bacteria, the rods being bacilli and the pairs and tetrads cocci, but not cyanobacteria because there's no evidence of pigmentation in this image (a separate post will deal with why the cocci are seemingly coloured at x100).

This was surprising because it is often said to be very difficult to see bacteria using standard bright field microscopes such as mine unless the bacteria have been stained. To be able to see bacteria without staining microscopists use specialist optics like phase contrast or dark field. But I don't think the resulting images are much better than I have observed here. So my question was, why can I see them so clearly? The best answer I have come up with is: Bacteria are difficult to see with bright field microscopes in water because they are the same brightness as water and the same colour (colourless). But I don't think these bacteria are floating in water, they're forming a biofilm. In biofilms the microbes produce a matrix of polysaccharides, proteins and extracellular DNA known as extracellular polymeric substance (EPS). So maybe the EPS is sufficiently different in brightness to the bacteria for them to be seen. I also think it helps that the bacteria have stuck to the underside of the cover slip because, as you can read here, this is one of the few circumstances where the image wouldn't suffer spherical aberration at x1000 magnification using an oil immersion objective. However, there's more to this biofilm than just bacteria and EPS.

Aquarium oily surface scum x1000. Bacteria, cyanobacteria, protozoa and plants.

The bland looking oily scum had turned out to be a rich community of microbes and small plants. I find it easy to imagine this thin film evolving into the foamy scums I see in areas of low flow, especially given an extra week to form. Maybe the membranous structure seen at x100 is this film of EPS/bacteria, fungi and cyanobacteria.

In this video it's obvious that the protozoa are underneath the bacteria stuck to the underside of the coverslip. It also shows that the bacteria can appear either as dark objects (as above) or light objects on a darker background. Depending on where in the field of view they appear.

In conclusion the foamy surface scum is indeed of biological origin.

Chapter 25. Resident from another order. Cyanobacteria identification 8.

Change in my aquarium comes slowly (if at all), so I was interested when a fluffy brown organism began growing on my bogwood.

W312. The brown fluffy organism attached to the bogwood is probably cyanobacteria from the genus Scytonema.

Previous experience suggested that it was some form of cyanobacteria (almost every sample I have ever examined from the tank has turned out to be some form of cyanobacteria) but it had some unusual characteristics that made me wonder. Most noticeably, during the weekly water change when I remove the bogwood from the tank and scrub it with a toothbrush, this organism remained attached. This was not true for any of the other species I have described, although the brown unicellular species can take a lot of effort to remove (Chapter 18).

Scytonema filaments sampled from an aquarium ornament (x100 magnification).

At x100 magnification a network of what looked very much like cyanobacteria filaments was revealed. But from which genus? Returning to "Freshwater algae of North America: ecology and classification" (Wehr and Sheath Eds) and specifically chapter 4 on filamentous cyanobacteria, I made the following identification. Q1-Heterocytes and/or akinetes develop commonly or occasionally in trichomes?

Scytonema filament with a heterocyte. Filament width 14.5 to 16.5 micrometers (x1000 magnification).

From reading descriptions of heterocytes (cells specialising in fixing elemental Nitrogen N2) I would say the cell in the centre of the above image is a heterocyte (heterocyst). It looks very different from the other cells in the filament as it lacks the brownish pigment and cytoplasmic granules. Notice the pores connecting it to adjacent cells are clearly visible. The presence of heterocytes is significant for two reasons: Firstly because it means that this species is from a different order of filamentous cyanobacteria to those previously identified which were all Oscillatoriales; Secondly, because it suggests to me that N2 levels in the aquarium must be very low indeed. I say that because according to "Freshwater algae of North America" the frequency of heterocytes along the filament declines with greater levels of NH4+ or NO3- and I see lots of heterocytes. So I can say that a species of cyanobacteria that is not only capable of N2 fixation, but that is actively fixing N2, has out competed the cyanobacteria/algae normally found on the bogwood (see Chapter 22) . Q2-Trichomes never branched or only with false branching? The branches below look like diagrams and pictures of false branching to me, so I say yes and that means this species if from the order Nostocales!

False branching Scytonema filament (x400 magnification)

Q3-Filaments with lateral false branches? Yes. Q4-Filaments isopolar, solitary, entangled in clusters, or forming woolly mats with common lateral branches in pairs (V shape), or rarely with single (Y shape) branch? I don't see lateral false branches in pairs, but I do see the rarer Y shape branches so Yes=family Scytonemataceae. Q5-Trichomes cylindrical up to the ends, apical trichome ends not attenuated, end cells more or less rounded? Yes=genus Scytonema.

Once again my aquarium has proven itself an ideal habitat for cyanobacteria, which seem to be increasing in diversity. Also, Scytonema provided a good first test of my new microscope and camera which have captured some beautiful detail I think. It's a shame that cyanobacteria look so manky from a distance.

Chapter 24. Cyanobacteria are unpredictable

I see it's been 21 months since I last updated this blog. The reason is that I still have a cyanobacteria problem. I was expecting the tank to transition to a healthy cyano free state at which point I would post the data I have been collecting relating the abundance of cyanobacteria to levels of phosphate, nitrate and pH. I wanted to make the point that cyanobacteria problems can disapear spontaneously with no input from the fishkeeper. But after 21 months there seems little point waiting longer. I wouldn't want to advise someone with a cyano problem to wait two years and see if it goes away.

W302. The Cyanobacteria is not as bad as it has been but, let's be honest, it's not great.

So here I am, cleaning my aquarium every week because it looks diseased and smells if I don't, while wondering what the point of cleaning my aquarium every week is. And all this happening while my unheated tank in the front room is cyano free. I replaced my unheated tank with a bigger one around 21 months ago (coincidently) and have never had any cyano problems with it. It seems to me that I should compare the two aquaria to see if anything can be learned about the causes of cyanobacteria problems.

My new unheated aquarium 5 months after start up and cyanobacteria free 

Chapter 23. Does using aged water result in a reduction in cyanobacteria in my tropical aquarium? #2

As I wrote in Chapter 22, by week 196 I observed filamentous cyanobacteria had returned to my freshwater tropical aquarium. I felt there was enough of it to test the ability of aged water (AW) to reduce its abundance. To re-cap, I had previously observed two occasions where the use of AW had apparently led to a reduction in the abundance of cyanobacteria. Firstly in Chapter XI (W112-W120)  where I saw a dramatic reduction within five weeks and almost complete disappearance within eight, and again in Chapter 21 (W148-W160) where I observed a dramatic reduction in 12 weeks. In order to replicate the conditions when I first used AW I used a brand new water container to mature the water.

I have to say, I was pretty confident it was going to work. And this third test would have been sufficient to convince me that keeping 20 litres of water heated to tank temperature and aerated for a week prior to adding to the tank was an effective way of controlling cyanobacteia (in my aquarium at least).

W197. Photo taken before the fist aged water (AW) change. The tank is in the early stages of a mixed Geitlerinema/Lyngbya infestation. 

W209. Photo taken before the twelfth aged water (AW) change. The tank is dominated by a Lyngbya infestation. 

However, it's obvious from the photos above that on this occasion, using AW has not resulted in a reduction in the abundance of cyanobateria in the tank. Indeed, the cyanobacteria problem has got much worse during the 12 weeks I used AW. Consequently I have to conclude that there is no benefit in using AW. This raises the obvious question, what was the reason for the dramatic decline in cyanobacteria abundance I observed between weeks 112-120 and again in W148-W160? And why were both these episodes followed by long periods where filamentous cyanobacteria were rare? The only macroscopically visible cyanobacteria in the aquarium were the brown unicellular types for 26 weeks following W120 and for 31 weeks after W165. Given that its disappearance seems to have nothing to do with using AW (and equally that its reappearance has nothing to do with using fresh tap water), I have to admit that after four years I am no further forward in understanding the causes of my cyanobacteria problem. Although I note the problem has changed subtly. During the first two years and three months the tank was in existence, I can't remember any occasions where the cyano died back spontaneously as it seems to have twice here. It is the cyclical nature of my current cyanobacteria problem that interests me. So my plan is to do absolutely nothing new and see if the cycle repeats. When that might be is unclear.

Chapter 22. An unloved season. Cyanobacteria identification 7

Regular visitors to this blog (if any) will know, that at some point after Chapter 21 (W160) I observed an increase in the abundance of cyanobacteria in my tank. Early signs were that a rapid return was likely.

W165. The cyanobacteria growing on the tank walls is a bad sign in my experience.

But the infection didn't take hold, when I syphoned off the mats on the gravel in the above photo, they did not re grow by the following week (W166). In fact the tank looked relatively cyanobacteria free for a long time. All photos taken immediately before water changes as always.

W190. Unicellular cyanobacteria in a freshwater aquarium.

Thirty weeks later by W190 (using fresh tap water for water changes for the previous 28 weeks) I could not honestly claim to have a cyanobacteria problem. This was the longest period that the tank had ever gone without one. There is obviously abundant brown unicellular cyanobacteria on the Amazon Sword and some on the gravel (there's even some growing on the tank walls near the gravel) but I did not feel there was enough to test if using aged water reduced it.  I began to question my belief that my fish-tank was fundamentally predisposed to the excessive growth of cyanobacteria.

W196. An inventory of cyanobacteria from a freshwater aquarium, see below for microscopic examinations of material from the labelled areas. 

I feel I should stress that I had not consciously changed my tank management practices in any way during the six weeks separating the taking of these photos. I continued the same weekly 37% water changes and gravel syphoning as for the previous 30 weeks. And yet by W196 there had been an obvious shift from brown unicellular cyanobacteria to blue green filamentous species. This is significant as it seems that these filamentous forms are much more capable of growing on the tank walls and gravel and consequently make the tank look far less healthy. In a way I was pleased as it gave me another opportunity to test if using aged water reduced the abundance of cyanobacteria. It also gave me the opportunity to test my belief that I can identify which species of cyanobacteria is growing in my aquarium from its colour and growth habits. Sample 1 has the lime blue green (almost turquoise) of species 2 (possibly Lyngbya, see Chapter 20), as does the species on the tank wall (Sample 3). The fact it can't grow far up the tank wall is also characteristic of species 2. Sample 2 intrigued me, it looks strangely green. I guessed it was some sort of mixture. Sample 4 has the dark blue green colour and tendency to form sheets around plants characteristic of species 1 (see Chapter XVI).

Sample 4. W196. The sheet forming cyanobacteria growing on the Java in mid-water is probably either Jaaginema or Geitlerinema.  

Sample 1

Sample 1. Scraped from an Ellodea plant. Unicellular (multiple species) and filamentous cyanobacteria (possibly Lyngbya) from a freshwater aquarium. The filaments are 8-10 microns wide. 

These filaments look like Lyngbya as identified in Chaper 20. I'm not surprised there is so much unicellular in this sample as, when I took it, it was clear the blue green mat was growing on top of brown material (see Chapter 18 for higher magnification images of the unicellular cyanobacteria).

Sample 3

Sample 3. Scraped from the front tank wall. Filamentous (8-10 microns) cyanobacteria (possibly Lyngbya).  

Again, very similar to the thick filaments in Chapter XIV and Chapter 20. I observed abundant evidence that these filaments have sheaths, which is a defining characteristic of this genus. Lyngbya is dominating the tank walls at this stage it seems as the sample contained little else . I notice now I upload this picture that there's a mystery filament running diagonally across the top right corner.

Sample 4

Sample 4. Sheet forming cyanobacteria sampled from a Java Moss tendril. Possibly Jaaginema or Geitlerinema. Filaments are approx. 2 microns wide.

I didn't take any good low magnification photographs of this sample but it consisted almost exclusively of the above filaments. They look very similar to the filaments identified as Jaaginema in Chaper XVI, but that I now think may be Geitlerinema (see below).

Sample 2

Sample 2. Scraped from the bog-wood. A complex mixture of cyanobacteria and algae? 

The sample was very diverse under the microscope but was mainly composed of all cyanobacteria species described here so far except the mysterious species 3 (Chapter XVI). There is also a new type of filament. The jagged filaments (there are three in this picture) are unlike the others. I could find no mention of cyanobacteria filaments articulating at the cell junctions in this way in either phytokey or the identification key I use. Notice how the species 2 filaments are laying on the glass slide like wet string. The new filaments move in and out of the focal plane of the microscope continually. This suggests to me that their cell walls have more rigidity and presumably are made of different stuff.

Sample 2. Possible algal filament, a eukaryote at last!?

One possibility is that they are algal filaments. If so the cells should contain discreet structures that contain the photosynthetic pigments called chloroplasts. There do appear to be flecks of coloured pigment in the above image so it's a possibility. It would explain why the bog-wood looks so green.

Jaagenima or Geitlerinema?

As you can see in this video, both the thick and thin cyanobacterial filaments are moving longitudinally. In Chapter XVI I identified the thin filaments as Jaaginema because they didn't move. Here I have to say they're more likely to be Geitlerinema filaments. It's possible that I used to have a Jaaginema infestation but now have Geitlerinema, which might explain why species 1 hasn't taken over the tank on this occasion  It's also possible that I have always had Geitlerinema in the tank. The description of Geitlerinema on algaebase sounds much more like what I have observed of species 1 than the Jaaginema description I posted in Chapter XVI.

Chapter 21. Does using aged water reduce cyanobacteria in my aquarium?

If using aged water (AW) did reduce the amount of cyanobacteria in my aquarium, if it is really was the factor responsible for the reduction I observed in Chapter XI, then I would expect it to do so reproducibly and over a similar amount of time. In Chapter XI I noted that I observed a dramatic reduction within five weeks, so for me to be convinced this time I would have to see a dramatic reduction over a similar timescale.

Week 148. Cyanobacteria (possibly green Lyngbya mats and brown unicellular cyanobacteria mats) from a freshwater aquarium. Photo taken Immediately before the first AW change.

As you can see, by week 148 species 2 was growing well on the Moss Ball and Amazon Sword but also on the tank walls, bog wood and gravel (the gravel was more affected at the far end of the tank). As I mentioned in Chapter 19, I was pretty efficient at removing it from the plants at this point and ruthlessly efficient at removing it from the tank walls and gravel, so most of what you see here will have grown in the week since the last water change.

Week 154. Immediately before the seventh AW change.

I could argue that there was less cyanobacteria in the tank at this point but I can't claim that the reduction had been dramatic. The bogwood was still almost covered and the Moss Ball. There was still cyanobacteria on the gravel and tank walls.

Week 154.

I think the best I can say is that the cyanobacteria problem hadn't got any worse, which is something because in my experience cyanobacteria problems always get worse. But there was little evidence that using AW is worthwhile. It occurred to me that one reason why it had failed might be the condition of the container I age my tap water in.

Week 149.

The inside had become almost entirely coated in a slimy layer of what I assume to be bacteria. So in an attempt to replicate the conditions when I first used AW and the container was new, I gave it a really good clean with a bottle brush and continued the weekly AW changes.

Week 160.

I think it's fair to say that over the next six weeks there has been a dramatic reduction in the amount of species 2. There is still some on the bogwood and gravel, but the plants are mainly clear, and there is none on the tank walls. Interestingly, the colonial unicellular cyanobacteria has returned on the Amazon Sword leaves. It's like the cyanobacteria succession I saw in Chapter 19 is happening in reverse. If that is true then over the next few weeks I should see a reduction in the brown unicellular mats. At that point I will switch back to fresh tap water in the expectation of seeing the succession played out once more.

Chapter 20. Cyanobacteria identification 6 (species 2 and 3)

This is mainly as an excuse to post more microscopic images of cyanobacteria, but I thought I would explain why I have started calling species 2 "possibly Lyngbya" and attempt to identify species 3.

Three filamentous cyanobacteria from a freshwater aquarium. Identified by an amateur at the genus level as;  Lyngbya (thick filaments), Jaaginema (sinuous filaments), and Romaria (short filaments).

From Chapter XIV (where I wrongly identified species 1), I know that species 1 is 2 micrometers wide because I measured some filaments under the microscope using eyepiece and stage graticules. By my calculations, depending on which photo I take measurements from, species 2 is somewhere between 8-10 micrometers. So, using the same key I used to more accurately identify species 1 in Chapter XVI, we get.

Q1. Are the filaments 3 micrometers wide or more?  A-Yes. Q2. Are the filaments cylindrical, long, sometimes constricted at the cross walls, but cells not barrel shaped or sub-spherical? A-Yes. Q3. Are the cells short, always shorter than one half the cell width? A-Yes. Then we come to the crunch. Q4. Are the filaments in vegetative state always without sheaths (if present formed only under stress)? Sheaths again! The problem is that the species 2 sample I examined in Chapter XVI  which showed clear evidence of sheaths, could have been stressed because it had sat around for a week. So I examined a fresh sample.

Filamentous and unicellular cyanobacteria from a freshwater aquarium.

No evidence of sheaths in this sample, but note the dark stripes along the filaments, it is at these necridia that the filaments fragment. I added some very small glass beads to the sample and vortexed briefly. The idea was that if I damaged the filaments I might see evidence of sheaths.

Fragmented sample of filamentous cyanobacteria from a freshwater aquarium.

It seems to me that the filaments have fragmented at the necridia. Many filaments now seem to have the remains of necridia at their end. This could happen if the filaments lacked sheaths so it doesn't tell me much.

Diatoms alongside unicellular and fragmented filamentous cyanobactera from a freshwater aquarium.

These fragments don't even have the remains of necridia at there ends. Maybe the fragmentation was too vigorous. What I really need is to slightly damage the filaments. Perhaps in the future I will find a way of doing that. But there is some evidence of sheaths here.

Fresh cyanobacteria sample from a freshwater aquarium showing evidence of sheaths.  Possibly Lyngbya.

So, if it's Q4. A-No to trichomes always without sheaths then it's Yes to "Trichomes in vegetative state always within distinct sheaths (only hormogonia and reproductive trichome segments can be without sheaths)". Q5. Do the filaments contain one trichome per sheath, forming mats? A-Yes = Lyngbya.  Of course it's possible that I have a mixture of species, some with sheaths (Lyngbya) and some without (Oscillatoria).

Possible Lyngbya filaments showing evidence of sheaths.

If you search for pictures of Lyngbya you will find some very similar images to the species 2 photos I have posted in this and other chapters.

Finally species 3. Q1. Are the trichomes less that 3 microns wide? A-Yes. Q2. Are the trichomes without sheaths or within simple, thin sheaths (when present always one trich/sheath) solitary or in mats, trichomes isopolar (both poles with same morphology)? A-Yes. Q3. Are the trichomes without sheaths, but may possess wide or diffuse mucilaginous envelopes? A-Yes. Q4. Are the trichomes straight, wavy, or irregularly coiled? A-Yes. Q5. Are trichomes mainly short, curved or irregularly coiled, usually only few celled, disintegrating , sometimes enveloped by an indistinct wide mucilaginous envelope, neighbouring cells occasionally disorganised? A-Yes (I guess) = Romaria. I can't find any photos of Romaria so I think I'm on shaky ground with this one. Correct me if I'm wrong.