Green dot algae

[John Rimbauer]

I've seen a few references to green dot algae being a common nuisance algae in freshwater aquariums, so I thought I'd try something out. A quick search of the site didn't show anyone else having tried it yet, so...

Depending on which references you read, people will claim that green dot algae is either caused by excessive phosphate, or by tanks with very low phosphate. I tend to favour the latter based on what I've seen in my tanks, but opinion isn't proof.

Currently, one of my heavily planted tanks has started growing green dot, whereas my other less heavily planted tank is clean as a whistle. They both have undetectable nitrate and phosphate levels, so I dose small amounts of potassium nitrate (KNO3) and trace elements to keep the plants ticking along. They are filled with the same water, and kept at the same temps, feed the same foods, have been set up the same length of time and so forth. It seems to me like a golden chance to test this theory, so here's my plan.

The currently clean tank is going to be kept as it is, functioning as a control. The other tank I am going to dose with small levels of phosphate to observe the effect on the dot algae. All other things - ferts, photo periods, water changes etc will be kept the same.

Hopefully I'll see the algae decrease, but I'll be just as happy if it proliferates. I'm not signed up with any image hosts, but if there's interest I could email some photos round to document the process.

[Adrienne]

I'll be interested to see your results

[Jennifer]

Evidence-based fishkeeping. Excellent.

[phoenix44]

I have green dot too. ill check for phosphates tomorrow and see what reading I get

Look forward to your results.

[breakaway]

I'm not signed up with any image hosts, but if there's interest I could email some photos round to document the process.

www.iforce.co.nz

[Caryl]

Email them to me if you like John and I will post them for you.

[John Rimbauer]

Email them to me if you like John and I will post them for you.

Thanks Caryl. I've been using imgur as a host, but lately I've found that they are very variable - some days hot linked images are fine, others they just plain don't work.

[oneeyedfrog]

How is this doing? any changes yet?

[John Rimbauer]

It's going well. Tentative results are written, but the photos haven't come out well. I'll make a point of posting my notes so far tomorrow - they're on my work computer.

[fishplants]

Great idea! I, too, have green dot algae in my established tank. My phosphate level in this tank is zip. Interested to see the results John. It tends to come and go over a long period of time. If I don't have a small amount of green dot, I have a small amount of green fuzz, if I don't have a small amount of green fuzz I have surface algae.

Amazing watching a mini eco-system and how the competition for resources goes on.

[Jennifer]

Agreed. My most balanced tanks have only have a small amount of green dot algae and are otherwise spotless. Often they only achieve this after some time of fiddling and battling other types of algae. I would love to be able to just be able to swing the balance and cultivate the stuff straight away.

[Caryl]

The only time I have been troubled with green dot algae is in winter when the sun is low enough to shine under the verandah and into the lounge so direct sunlight (albeit weak winter sun) hits the front tank glass for a couple of hours or so a day. I get the spots in a small area of the front glass only, where the sun hits.

[Jennifer]

Regardless of how much you have, if your tank grows green dot, then there is a really good chance that the other forms of algae are minimal.

[fishplants]

Regardless of how much you have, if your tank grows green dot, then there is a really good chance that the other forms of algae are minimal.

Definitely agree with this. I even have a small amount of dreaded Blue Green Algae (BGA) in my tank, it has been there for at least the last 6 years. It only grows below the gravel level at the front of the tank, where the glass 'transports' a small amount of light down about 6mm below the gravel surface - it comes and goes as well. It never comes above the gravel surface - well not since soon after the tank was setup and it covered absolutely everything!

[John Rimbauer]

OK, the pictures came out rubbish, so we'll have to go old school and use text.

Raw results from my notes:

Day 5 – the green algae on the front of the tank seems larger – have marked and measured a dot at 3mm, to compare on subsequent days. Green dot algae on the back of the tank seems to have declined – looks clearer than previously.

I have also completely cleared a section of glass, so that I can see if new spores are settling and growing.

Other obs – the java fern’s roots are showing a lot of new growth. Tips are white indicating a new growth cap has formed, and lots of root hairs are visible just behind the cap.

Day 7 -Green algae on the back of the tanks has continued to decline. The algae on the front of the tank has not increased in size, based on measurements of reference colonies. The edges of the colonies are also starting to look ragged, as if it were growing unevenly, or perhaps flaking away or being scraped off by snails or catfish. Previously this was not apparent; the colonies grew in a circular fashion.

The clean patch has no visible regrow, even with quite meticulous examination being done.

Day 9-Reference colonies have not increased in size. The back glass looks cleaner than previously. The colonies on the front of the glass have a distinct ragged appearance, like they have been nibbled. Some of them have lost the algae from the centre, leaving either a ring shape, or more a “pac-man” shape where an entire segment has been lost. There are a couple of colonies lower down near the substrate which look more healthy, but most are ragged and small.

Other obs – ambulia has started striking roots from some of the nodes near the surface. E. osiris has developed a much stronger red colour on the new leaves. Java fern is growing new plants at some of the leaf tips.

Day 12 - Green algae on the back of the tank is difficult to spot. The colonies on the front of the glass are looking very ragged and eaten, it is obvious that some of them have almost completely gone. Several colonies look healthy, but the reference colonies have not expanded in area. The clean are has no sign of any colonies forming.

Day 20 - Reference algae spots have gone although there are still some tattered colonies in the area. None are larger than approx 2mm. Back glass has a very few, very small colonies of algae which are no longer visible without careful observation. The cleared area has no colonies visible, even with careful inspection.

Overall plant growth is heavy, the tank will need to be pruned which may have some impact on the algae one way or another.

[John Rimbauer]

And a bit of discussion.

The green dot algae more or less stopped expanding as soon as the phosphate levels were raised. A few colonies grew after a fashion for a short time, but nothing like what they were doing previously. The existing colonies were damaged by snails and bristlenose cats and declined over time. The area I cleared never grew any more green dot, which suggests that the elevated phosphate level stopped it dead - I can't comment on the methodology of that. Maybe stopped it sporulating? Or the growth was limited by higher phosphates?

The glass at the back of the tank cleared very quickly compared to the front. The back gets more light than the front in this setup, as the plants are pushed away by the flow from the spray bar.

The other plants grew very rapidly during this test. This makes me think that the phosphate level was effectively limiting all plant growth in the tank. This supports the theory that very low phosphate conditions are more suitable for green dot algae.

It would be interesting to ramp up the levels higher than I did, but I didn't want to complicate things. I just replaced 1/4 of my tank change water (approx 10L) with high-phosphate tap water.

There was no sign of any other algae in the tank during this test, even though the tank has had BBA, staghorn, cyano, and green water before.

Conclusion - green dot algae grows best in very low phosphate conditions in a planted tank, and can be inhibited, but not killed, but marginally elevating the phosphate level. The overall level in the tank never measured on a phosphate test kit.

[fishplants]

Hi John,

very interesting findings, thank you for your thread. It would be interesting to get your water parameters, especially the phosphate levels. While this approach may work for that particular tank, it may not work for another tank with differing parameters.

It does sound like your plants have really benefitted from the addition of PO4, which is probably the real reason for the reduction in algae - as the plants take advantage of the increase in a previously deficient major nutrient, they also use more of other major and minor nutrients (which may have been in relative abundance) to the detriment of the algae.

It may actually be that the algae utilises the relatively abundant nitrates, or potassium, or iron, or ?, and putting PO4 in balances things out.

My approach (guesswork?!?!) is to throw more ferts into the tank if I have algae, based on my assumption at the time of which one/s I think is/are deficient - or, if there is sufficiently good water parameters, then more plants will do the trick.

[Aquila]

I have no idea what my phosphate levels are at, but I only grew green spot algae on my glass when my lights were on for 12 hours as opposed to 10. It started growing when I added another 2 light tubes for a total of 4. I would clean it off and then it would just start growing back. It also only grew on the glass that was most exposed to light (aka not shaded by plants). When I reduced the light period it never come back, not even in the especially bright areas.