Blue-Green Algae

[Kaidonni]

So, every tank has algae. I'd like to think I have mine under relatively good control, having 7 hours of tank light a day and not having algae explosions. I do have some green spot algae (lack of phosphates?), and have noticed brush algae on the roots of newly sprouting java fern, but apart from that, a quick brush of the standard brown and black algae that appears on the glass during my 50% weekly maintenance and the issue is resolved. Some of the brown and black algae does grow on the plants, so I might have a light/nutrient imbalance there, but it isn't runaway or anything severe.

Except...today I noticed that, on those same baby java fern, there was something that resembled what I can only assume to be blue-green algae (should have taken a photo - too late now, removed most of what I could definitely see, so I might be identifying it incorrectly). It must've been a few days growth at least, if not more, and it was growing over the roots/brush algae. I look at my tank everyday, but missed this until this evening. I tried taking baby java fern off of the plant most infected, but in the end tore out the whole plant because I didn't want to take the risk. I did what I could with the other java fern from what I could see and where I could reach, but I'll have to keep my eye on it over the coming days and perhaps tear out the infected plants on the weekend when I have time to get into the tank, mess about, and plant new ones (mess about too much, and it kicks up particles and debris - better to do it during a water change).
 
I have scraped algae off the filter housing during some of my water changes, but I don't think it's blue-green (a little too hard to remove, isn't blue-green algae meant to be slimy and come off easily?).
What might cause blue-green algae to start appearing? I'd like to think my water is clean enough, with a 50% water change every week - which involves a gravel vac and filter clean - only three White Cloud Mountain Minnows at present, and a live planted tank. Temperature is ranging from 22c/23c-24c/25c (heater not plugged in). I feed every other day, and feed sparingly. Most recent water tests for ammonia, nitrites and pH were a week and a half ago (25th July, all fine), nitrates about the 13th July (~30-40ppm). I avoid testing in the week due to less than favourable light conditions in the evening - no time in the day due to working - and I refuse to use artificial lighting for testing purposes, so I can't really take my time and test as carefully and attentively as I like to until the weekend (I do not like rushing the tests, and often re-do them when I become worried I mis-read them). Total Dissolved Solids were ~305ppm around the 13th July, I suspect this to be a mix of my temperature matching and use of Prime/standard tap water quality.

Could it be phosphorous? Too much light (7 hours a a day, as I mentioned above)? I don't add any nutrients to the tank, and don't do badly with java fern, vallisneria and amazon sword plants - am I starting to hit an imbalance between nutrients and light? Possible plant from my local fish shop infected, and it's passed on to the others in my tank?

 

[Byron]

This doesn't sound like cyanobacteria, which is what "blue-green algae" really is, a bacteria not an algae.  But it is very slimy and easily comes off most any surface with your fingers.  It is caused by high organics in the presence of light, nothing else in spite of what one may read here and there.  Anyway, it doesn't sound like what you have, so be grateful, as cyanobacteria can be difficult to completely eradicate.
 
So assuming this is some type of algae, I can say that all green and red algae are caused by light and/or nutrients.  Obviously the latter will be present in any aquarium with fish, so it is generally the light that controls the algae.  In planted tanks we aim to balance light intensity with nutrients to benefit the plants but not encourage algae.  If either becomes more than what the balance needs, algae takes advantage.
 
The brush algae on Java Fern is a common problem when this plant receives too much direct light.  Keeping it under a layer of floating plants, or somewhat in the shadow of other tall plants, usually works.
 
I might be able to pin this down more if you can provide the light specs (the intensity aspects, and spectrum).  We can vary the duration of course, but this only works if the intensity itself is reasonably close to what the plants can use in balance with available nutrients.  More or less duration does not compensate for too much or too little intensity, but reducing duration can work when the intensity is not too high to begin with.
 
Your nitrates are high, they should not exceed 20 ppm, and preferably be lower.  This in itself is not causing algae, but it is indicative of organics/nutrients being high and this certainly is part of the "balance" issue.
 
Photos will help if you can.
 
Byron.

 

[Kaidonni]

As mentioned above, it was too late to take photos, I'd already removed the offending plant and algae.
 
As to nitrates, I'm afraid my tap water limits me very much in how low I can get it, we've covered this in previous threads. The 2013 reporting year puts my tap water nitrates between 19.3-33ppm. I won't be going for reverse osmosis, which is the only recourse to get it any lower. I say 30-40ppm also because the tests aren't entirely reliable, I expect some degree of error in them. All I can say with certainty is that the tests have been coming back orange since June, and are far better than they used to be.
 
As to the light specs - Sun-Glo 46cm 15w T8, on for 7 hours a day from 2pm to 9pm.

 

[Byron]

I think I remember this is a relatively small tank, so my first suggestion would be reducing the duration of the light by an hour.  After a few weeks, if no better (remember the algae that is there will not go away, the aim is to not have it increasing and that is the sign the balance is better) reduce another hour.  Adding more fish will also likely help as they are the prime source of nitrogen for the plants (ammonia/ammonium).

 

[Kaidonni]

Yes, it's 50 litres - well, that's what I estimate the volume to the level I fill, the filter, airstone, fish and plants have to be accounted for (so I'd say somewhere in the 47-49 litres range).
 
I was thinking of reducing the lighting hours myself, although mainly because with the darker nights coming, should I not be around, it'd be useful having the light go off before it gets dark.