Blue Green Algae and Diatoms?

[robfromdublin]

Hi all,

I am making my first foray into keeping fish and have gone for a planted tank. I've been doing a lot of reading around the subject but am confused by the problem I have at the moment. I appear to have BGA caught up in my java moss and yet in another section of the tank have a brown, dust-like substance that look very much like diatoms. I'm basing these algae identifications off James' Planted Tank website. I also have some green algae that could be hair or oedogonium but relatively little of this and it doesn't really concern me.

Below is an overview of my setup. I will add pictures but my attempts to take some clear ones before running out the door this morning failed.

4ft tank (4'x1'x18") 2nd hand but running for 2 months
2 38W T8 bulbs (Arcadia Freshwater & Tropical; ie one 'normal' and one for plant wavelenghts) on for 8 hours
Eheim 2215 filter
Sand substrate (came with tank, don't know composition but pH is 6.8 so probably not calciferous)
Dose Easylife Profito and EasyCarbo (2ml & 3ml per day, respectively)
No pressurised CO2 or macros
Fish: 6 Sterbai cories & 2 small bristlenoses (pretty light bioload for tank)

Plants:
Elodea densa - initially did very poorly but doing better of late. Still not growing quickly though (blame the easy carbo) and is lightly covered in what i think are diatoms
Hygrophila polysperma (i think, based on pics) - growing quickly but some yellowing of leaves near surface
Java Moss - has attached itself to bogwood but choked by BGA now
Java Fern - growing very well
Echinodorus Peruensis - 1 of 5 plants died. others not growing particularly well but have perked up in last fortnight since i put some potting compost under sand at their roots.
Dwarf Hairgrass - not growing quickly but not dying. seeing signs of new leaves but at this rate will be a looong time before it carpets
Duckweed & Amazon Frogbit - both growing very well

I would describe the tank as lightly planted.

Have tested nitrates and they appear to be zero. Although the test kit also tested the tap water at zero which according to the water company generally has 3ppm. Nevertheless because of the BGA I have got some KNO3 and will experiment with it.

So my questions are: given some of my heavy nitrate removers (duckweed, hygrophila) are doing well, as is the Java Fern which is easy, are my nitrates really zero? Could something else be causing my algal problems? From some reading today I realise my filter may not produce enough flow, but is that critical in a low-tech aquarium where growth is not that quick?

I will post up some photos when I can sort my camera out.

R

 

[ceg4048]

Hi,
Welcome to the forum :!:

If you are enriching your tank with Easycarbo then this counts as CO2 injection, therefore the tank no longer qualifies as "low tech". Any carbon enrichment drives the plants to uptake more nutrients than they would do otherwise. Therefore you need to supplement NPK more than you would if this were truly a low tech (non-CO2) tank.

BGA is typically caused by low NO3 so you just need to add the KNO3 and this issue will subside. You'll also need to dose PO4 so either a dry powder such as KH2PO4 or a commercial Phosphorous product is necessary.

The nitrate test kits are not consistently accurate so the number is unknown.

Adding NPK will address most of your issues. Your lighting is not over the top. Flow is always an issue so it's a good idea to follow the 10X rule whenever possible.

Cheers,

 

[robfromdublin]

Thanks ceg,

I was wondering about PO4 alright. Given my tap water comes in at about 1ppm PO4, do I really need to dose it if I'm keeping up water changes? By adding just NO3 I'll be bringing the tap water into line with Redfield. This is my thinking anyway. What are your thoughts on that? I take it that potassium isn't a problem as I'll be dosing KNO3? Also the profito has potassium in it so I think I'm covered there.

Here are the photos anyway. For those reading please feel free to point out any potential problems!
Tank:

BGA?:

Diatoms?:

Is this Hygrophila Polysperma and might the yellowing be nitrate deficiency?:

 

[ceg4048]

Well, I mean it only matters what your algae think. Rhizo thinks that you don't have enough nutrients/CO2. The BGA and those yellow leaves think that you don't have NO3. I never concern myself with what the tap supposedly has in it because the proof of the pudding is in those photos. The path is clear. Remove by hand as much as possible as much of the algae that you can. Implement large water changes 2X or 3X a week and start dosing macros along with your traces. In a few weeks you'll wonder what all the fuss was about.

Cheers,

 

[robfromdublin]

Good point, thanks for your sage advice

 

[robfromdublin]

I've been dosing nitrate and doing large water changes but I still have a problem with some elements of BGA and loads of diatoms still caught up in the moss. I've been holding off dosing phosphate as a cost-cutting measure but am starting to see some green spot algae now, so I will probably start with mono-potassium phosphate.

I think flow could be an issue. I have an Eheim 2215 advertising 620l/h (so probably about half that) and 2 air stones. The outflow for the filter is above the central java fern in the above pic, at the back and pointing away from the intake. The first air stone is just above the intake and the second is just to the left of the java fern. Some of the moss is moving in the flow from the air stone but it doesn't appear to be doing anything to get rid of the diatoms.

Is there anything I can do with my existing setup to improve flow? If I were to buy a powerhead, where would I put it? Which is a more effective use of funds (PO4 dosing or powerhead)?

 

[ceg4048]

Hi,
I would suggest that you stop using an airstone. These tend to drive off CO2 which may be counter-productive. If cost is an issue and a stronger filter is not feasible, then point the powerhead in the same direction that your filter outlet is pointing. Cost cutting PO4 only cuts your chances of success to nearly zero. Adding PO4 enables a higher Nitrate uptake.

Try a three day blackout. Cover th tank with black plastic bin liners. Stop the Easycarbo dosing but continue nitrte and PO4 dosing for the three days. Dose only at night so that no light gets in. At the end of the period do as large a water change as you can and then resume easycarbo and nutrient dosing.

If the BGA returns after this then it means you need more nitrate.

Cheers,

 

[robfromdublin]

I actually have already done a 3 day blackout, although without dosing nutrients as I was away. It killed the BGA but I've noticed the BGA is starting to creep back in. I'll get myself some PO4 so.

Surely the CO2 just equilibrates more quickly with the atmosphere if you use an airstone? Which drives off CO2 if you inject it, but draws down CO2 if you don't and your plants are creating a pCO2 gradient? That's why I figured it would be OK to use one.

 

[sWozzAres]

Personally, I would just have the airstones on for an hour or so, and go off right before the CO2 comes on. Assuming you are running good CO2 as the lights come on. You will lose some CO2, but so what, the extra O2 is always a welcome benefit to the fish especially as the CO2 is building up to maximum levels at the same time natural O2 is at it's lowest.

 

[ceg4048]

I actually have already done a 3 day blackout, although without dosing nutrients as I was away. It killed the BGA but I've noticed the BGA is starting to creep back in.

OK, so this means you're either not dosing enough NO3 or your flow is weak, or both.

Surely the CO2 just equilibrates more quickly with the atmosphere if you use an airstone? Which drives off CO2 if you inject it, but draws down CO2 if you don't and your plants are creating a pCO2 gradient? That's why I figured it would be OK to use one.

Think about what happens if you continually shake a coke bottle. The more you agitate the liquid the more CO2 escapes. Fish produce CO2 that would ordinarily help raise the level, but no, you're sending it right out the window with your bubbles. The only good bubbles are dead bubbles...or CO2 bubbles.

Cheers,

 

[robfromdublin]

Well that's only because CO2 is super-saturated in coke, and so agitation allows the CO2 travel along the concentration gradient, and outgas, more quickly. I was speculating that the CO2 gradient in my tank was from the atmosphere to the tank, which would be the case if the production of CO2 by fish is less than the uptake of CO2 by the plants. In that case, using an airstone would be advantageous. Although now that I think about it, by using it in the early part of the photo period I'm driving off any CO2 that would be accumulated through respiration in the night. So really there is only a case for doing it towards the end of the photoperiod, and only if the sink of CO2 from plants is greater than the source from fish.

I was dosing 1ppm nitrate per day as per PPS-Pro but today I've dumped in 5ppm and I'll keep that up for a while to see how it goes. Monopotassium phosphate has also been ordered. Payday on Friday so I'll look to get a powerhead then. Is there any recommended makes? I've already ticked Koralia but there seems quite a lot of other makes out there.

Thanks again ceg

 

[ceg4048]

CO2 is always being produced by everything that is alive in the tank, including the plants and some bacteria. That means the concentration gradient, if left alone will always be from water to air. We have a hard enough time preventing that. Adding more agitation speeds this escape up. The supersaturation of coke only explains the ferocity and speed of the outgasing. The principle is the same. Similarly, plants produce oxygen and oxygenate the water. There is therefore an oxygen concentration gradient from water to air. Bubbles accelerate the outgassing of this extra oxygen as well, so you're not doing yourself any favours at all with bubbles. Only when the O2 content of the water is low due to consumption, such as late night or early morning are bubbles advantageous in this respect.

Cheers,

 

[robfromdublin]

You're saying that bubbles help replenish oxygen at certain times because at those times O2 is being consumed, ie there is a net uptake of oxygen. In exactly the same way, at certain times there may be net uptake of CO2. At those times it is possible that surface agitation would be a help. I'm not saying this is definitely the case, there are a lot of other variables at play (eg the probability that a CO2 molecule gets outgassed after respiration, the probability that a CO2 molecule gets used in photosynthesis after respiration), but theoretically it is possible. That is why, for example, the biological pump works in the oceans, drawing CO2 out of the atmosphere; at certain times there is a net uptake of CO2 in the upper ocean.

On the balance of it I'd say that the chances of that happening are slim, and it would be extremely difficult to test, so I'll be turning off the airstone. Hopefully the decrease in flow is made up for with the increase in CO2 at the beginning of the photoperiod.

 

[dw1305]

Hi all,
I think you are right that the more surface turbulence there is the greater the surface for gas exchange, this is one of the reasons that the aerobic treatment of sewage uses trickle filters, there you have a very large surface area of bacteria holding media with a thin film of "water" flowing over it, the thinness of the film means that both CO2 can out gas and O2 diffuse in. In this case we can assume the tank water and inhabitants has a relatively low BOD, so we need to look a the solubilities of O2 and CO2 in relatively pure H2O. For the aquarium inhabitants there is also the "Bohr effect" to take into account : "an increasing concentration of carbon dioxide will reduce the oxygen affinity of haemoglobin." If we have efficient gas exchange, either by water movement or filter design, as well as oxygen dissolving into the water, CO2 will dissolve out until it equilibrates with atmospheric CO2 levels (about 0.03% of the atmosphere). Unless we are physically adding CO2 to the water, water movement, and trickle filters, will add CO2 to the water when plants are actively photosynthesising (utilising CO2 and producing oxygen), and out-gas CO2 when levels in the water exceed those in the atmosphere. Typical CO2 levels in tank water are dependent upon temperature, pressure and the carbonate content of the water, but should be in the range of 1 – 2ppm (this is not even close to the maximum amount of CO2 that plants can utilise, the 30ppm from earlier in the post is x60 the natural level).

Oygen is much less soluble than CO2, meaning that for an air pump the bubble size is also important, in that the smaller the bubble the greater its relative surface area is, and the more diffusion of gas into the water will occur. This means that an air pump needs to produce very fine bubbles (in the range of 10 – 200 microns diameter), that have a long “residence time” in the water column, if significant exchange of oxygen to the water is to occur. For maximum residence time and effect, unless you have a “wet and dry” or bio-wheel filter it would be advantageous if the filter intake picks up both the bubbles and oxygenated water, and feeds them straight into the filter where they will provide much needed oxygen to the nitrification process.

Oxygen solubility (milligrams O2 per litre) at mean sea level & standard atmospheric pressure (STP) 1013millibars (mb) is 8.3 mg/l at 24oC and 7.3 mg/l at 32oC. Carbon dioxide solubility is quite a complicated equation (Henry's law <http://en.wikipedia.org/wiki/Henry's_law> and the carbonic acid / carbonate equation both need to be taken into account) probably best shown graphically.

But as you can see the effect of rising temperature on solubility is quite striking.

cheers Darrel

 

[robfromdublin]

Blinded with science! Nice post

One thing is that the %CO2 compared to atmosphere should be more like .3%? If the 1-2ppm CO2 is roughly correct for the average tank (bearing in mind the large variance this could have due to carbonate hardness and temperature). I was wondering about what that value was actually (concentration of CO2 in a freshwater tank without injection).

Is there any info out there on equating liquid carbon like Easy Carbo to CO2 concentration in a tank in terms of photosynthetic ability? ie 10ppm of easy carbo is the same as having 5ppm of CO2. Would be interesting to figure that out although I don't actually know what is in easy carbo other than 'photosynthetic intermediates'.

As an aside, while it would be advantageous for a filter to pick up bubbles along with tank water (to provide oxygen for nitrification), this may affect the siphon action of your filter. Mine gets very noisy whenever it does pick up a stray bubble

 

[dw1305]

Hi all,

One thing is that the %CO2 compared to atmosphere should be more like .3%?

No, it is right although it should have been 0.04% really, "As of April 2010 carbon dioxide in the Earth's atmosphere is at a concentration of 391 ppm by volume, the pre-industrial level was about 280ppm." I think I got the 1 - 2% CO2 levels for Aquaria from Brett, the "Skeptical Aquarist", but I don't know where he got them from. I cut and pasted them, in this thread, from here <http://plecoplanet.com/?page_id=829>.

You are definitely right about the trapped air bubbles being noisy, the best filters in terms efficiency in treating a large bioload are wet and dry trickle filters, but they are even noisier. You really need a good flow of oxygenated water for canister filters to work efficiently, so as long as the bubbles are small they should go through the filter with out becoming trapped.

I'm not sure that you would be able to equate any of the liquid carbon supplements with CO2 as a direct comparison. You would have to do it experimentally by constructing a CO2 standard graph (by measuring the mean yield and confidence interval for a number of replicate plants of any species grown along a CO2 concentration gradient), and then (leaving all other parameter the same) substituting the CO2 for a carbon supplement, measuring yield and reading the equivalent CO2 value from the standard graph.

Would be interesting to figure that out although I don't actually know what is in "easy carbo" other than 'photosynthetic intermediates'.

it is glutaraldehyde, but I'm not sure any-one knows quite how it works yet.
There have been a few threads about it.

cheers Darrel

 

[robfromdublin]

Well I've been dosing EI and doing my water changes and still the algae persists. Also the plants have started to show signs of potassium deficiency (put dwarf anubia in 10 days ago and a couple of holes are appearing in old leaves), which I was surprised at. I've decided to try to remove the duckweed from the tank as I'm taking out handfuls of it and I think it might be starving the other plants. Just gonna try to remove as much as I can each day and hopefully it'll disappear, or be more easily managed, before long.

The other major factor is flow. I measured it during a water change yesterday at ~150 l/h, which is a miserly 1x turnover. So I'm thinking a powerhead would be a good investment. Hydor Koralia 1 is rated at 1500 l/h and a shop near me sells it for <£30 so I'm gonna go with that I think. Will be interesting to see if flow is the missing link in getting a nicely balanced tank, and indeed if it is the reason for apparent signs of deficiency in the plants.

 

[dw1305]

Hi all,

I've decided to try to remove the duckweed from the tank as I'm taking out handfuls of it and I think it might be starving the other plants. Just gonna try to remove as much as I can each day and hopefully it'll disappear, or be more easily managed, before long.

Duckweed is very efficient at converting nutrients into biomass, so as you remove it your fertiliser addition is being exported. Both Lemna minor and L. gibba are widely used in the industrial scale treatment of nutrient rich effluents. Here is a link to some of Diana Walstad's research. <http://www.aquabotanic.com/plants_and_biological_filtration.htm> and I've got a lot of papers, here is the abstract of some Dutch work:

Zimmo, O. et al. (2004). "Nitrogen mass balance across pilot-scale algae and duckweed-based waste-water stabilisation ponds" Water Research 38:4, pp. 913-920
Abstract
Nitrogen removal processes and nitrogen mass balances in algae-based ponds (ABPs) and duckweed (Lemna gibba)-based ponds (DBPs) were assessed during periods of 4 months, each under different operational conditions......... N uptake by duckweed corresponds to 30% of the influent nitrogen during the warm period......."

cheers Darrel

 

[ceg4048]

Hi,
You haven't really stated exactly how much of what you are dosing. Holes in leaves are typically due to poor CO2/flow, not low K.

There is no point removing a plant because you think it is feeding more than others. The solution is to add more nutrients/CO2 or more flow. This is not to say that you should never remove a plant if there is a good reason, such as it's becoming invasive or that you simply don't like it, however your stated reason is definitely not a good one.

It is much less likely that your duckweed is "stealing" nutrients from other plants and that it simply is a better feeder than the others. Is it at the surface? If so then it has access to much more CO2 than the other plants and can produce more carbohydrates than the other plants. When a plant produces high level of carbohydrates it can then make much better use of Nitrogen and other nutrients.

If you're still getting BGA and Rhizo then you need to clean the tank really well, including the substrate, while doing a large water change. Clean your filter, add more flow, add more EasyCarbo and add more nutrients.

Cheers,

 

[dw1305]

Hi all,

Is it at the surface? If so then it has access to much more CO2 than the other plants and can produce more carbohydrates than the other plants. When a plant produces high level of carbohydrates it can then make much better use of Nitrogen and other nutrients.

That is a major reason for the efficiency of Eichornia and Lemna based biofilters, because these plants float, they have access to both aerial CO2 and maximal PAR and the turbidity/ depth of the "water" isn't an issue.

cheers Darrel