blue-green is possibly cyanobacteria rather than algae.
a good article is linked below to explain causes and cures for different algae problems. if cyanobacteria, you can black out the tank for a few days, increase nitrates or treat with antibiotics at half-dose. maracyn brand should work.

Here is a link that might be useful: algae in the planted aquarium

treat it with maracyn. I've used this method a couple of times before and it worked so well

Jeff is most likely correct but this bacteria also grows in different colors in different environments (just did extensive research after my corries I've had for years started to die with no obvious symptons until one would go to top of 75 for his air gulp but could not right him self on the way down - drifting as if stunned upside down (ruled out whirling disease as I'd seen it), including his link provided and more direct scientific - lovely site mho)... this was after I for the first time ever - 45 plus years had this algae growing on my java moss (on branchy wood on suction cups). (see email sent to forum member - his was fin melt and need for water testing even for very experienced - me too!

Never take anything - like water out of tap, for granted lesson learned.) Water chemistry is the key with this algae/bacteria form. (reason why I think even after treatment it keeps coming back for many.)

Erythromycin found in Mardels product (Maracyn One) will take care of it pronto. But you may wish to tank the fish so on out so as not to dose them ie resistance can build up and all meds cause some degree of harm.

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Bascially, for me it was a confluence of factors. Ie, high heat and phosphates dumped in by muncipality to deal with increased load of bacteria - research showed it increases in the summer to fall cycles in the wild (all algaes are important in nature including this nitrogen fixing one in rice paddies) (and another clue as to how it can affect water chemistry, esp in diff ph/hardness) (N to P ratio crucial for this bacteria) (also redox and other water chemistry articles that go beyond the norm).

(read below email for all factors I discovered in my little slice of "nature" gone much awry!)

Turns out I had read (at the above and other links) about this bacteria (thanking my blessing for NEVER having had it - guess I forgot to "knock" on wood, lol) and knew it can cause neurotoxicity (aquaculture and vet sites go into more depth.)

(see links below)

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The idea is to correct all underlying causes... and it will not come back - so far mine has not. (the medication worked with one dose but I have a simple arrangement so that my maintenance is lower keyed, ie all wood can come out, no soil or plants that need it save for small layer of sand/gravel and Anubias)

Best Sherry

Here is the email... not edited for lack of time.

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SAD SAGA continued - corries dying and solution.

After two died with NO apparent visible signs of anything......

Then, one would go to the top of the 75 (very lightly stocked, over filtered and long established) but would float upside down to the bottom... after observing this again and again, I took the remaining corries out and put them in a darkened hospital tanks and started a general (suspecting bacterial something or other)....treatment - light salt and Mardel's Maracyn-Two two (because of it's "abilities to be absorbed by the fish through the skin which was great for bettas with obvious bacterial septicemia ie bloody streaks - and the level's rise during treatment ie it can assist with internal bacteria - gram negative type which most are.... drug is minocycline...)

(see med link below)

(It has excellent anti-inflammatory properties which makes it a good choice for septicemia, although for Viral Septicemia there is no effective treatment, only prevention. Minocycline is also effective for fin/tail rot )

I did this because due to years of "treating" or trying to, hundreds of "rescue" bettas (no more now) I've seen it all and narrowed it down to a few things and it is usually bacterial and long internal at the point I receive them.

This would hopefully give me some time to do some serious research...

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Within short time however (an hour or so) the little guy stopped floating back down upside down! Hmmm thought I.

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I like you, with decades of experience, judge my water quality from the smell and other reasoning. I have a lot of wood in that tank so there is some organic quality to it, I over filter and change one of two each week, and do more frequent but smaller water changes (once a week.)

Do to the neighborhood I once had a massive almost immediate die of of fish in a huge (50 gallon) globe after a water change where unlike usual, I did not let it get filtered for more then one day or more. I ran to the local pet store two blocks away, and the manager was in a rage as all of their fish were dying (did a water change that day as well.) I live where that crane crashed and that day they were doing pipe work and who knows what toxins got into the water system. All my fish died and the larger gourami I put down as he was sufferning after a day of my trying in vain to save him.

Hidden water chemistry gone awry but I got extra chem remover for my filtering aging water (garbage tub) and wait two days now... so rule that out. (we as well on the East side midtown get sewage backing into water supplies when it rains in huge volumes.)

And none of the other fish were acting differently (at least not yet thought I but something was up.)

I knew as well that by the time we "see" or observe symptoms things have been brewing for a while.

But now, I got out my tests kit - and was stunned. And a big oops (and learning lesson for me.)
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Normally, my tap water comes out at a very low yellow ph of 6 or even less. (a decade ago it would stay that low in my aquariums, so I would have to add (baking soda) so on to raise it.

Then due I am sure from additives to the muncipal water additives, it shifted drastically. It still came out at 6.0 and stay there even when sitting or filtered (did extensive test way back when, with different sands - one brand is actually left over mining sludge coated with epoxy! )

But, in the tanks it eventually rises to hard water (at one point so hard it was off the charts!) and higher ph - top of the card scale of 7.8).... this is in spite of lots of wood, nada, huge volumes of peat (gallons in water treatment) and nothing in the scape that would add minerals to the water. I have a diy co2 and water still high.

For years, the fish have had no problems and when I (used to - downsizing) buy them from a local pet store their water in their tanks being soft (6.0) I would take extra water home (gallons) and slowly acclimate my purchases to my water (about one day).

So when I tested the water in the 75 I was stunned as nothing had changed regarding scape hard or soft but the water tested at 6.0 or even lower!

Now that in itself (since I assumed it occurred over time and I never do larger water changes).... water changes btw should never be more then 1/3 as even bacterial change can cause shock and stress leading to disease, even in an emergancy better to do one partial then start a day long dribble - dribble out (airline tubing knotted to control drip rate) and dribble in of fresh water.)

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Other factors I took into consideration. I had just sold my wood (thanks to Mark, on this site) and had trimmed about three quarts of java moss to give to the person who purchased the wood. That was the only "plant" in the aquarium at this time. (was some narrow leaf java ferns but after years of going strong they had "wilted" back to rhizome.... hmmmm?)

For the first time in my aquarium life (45 years plus) I noticed some blue algae... ie Cyanobacteria growing at the top of the wood (my brancy wood is going from top of tank downward (attached with suction cups and filter holders to shape direction) as in river bank with "fallen" branch effect, lol) so the moss is planted at the top areas about midway down with no moss on finer pointed ends which float above the light layer of gravel/sand bed (for bio culture and cory needs only ie no plants.)

At first I just took the wood out and kind of rinsed it while I did serious research on this bacteria algae as I had spoken with Dr. (Aukmen? forget now and not looking up due to time) at Natiional Fish Pharmeceuital re his research on red algae - related (Cyanobacteria can come in all colors and fresh/salt water.

As well years ago when researching bio cultures, I was greatfully allowed to pick the brains of another Doctor who was at a company and spoke at great lengths about algaes and sub forms and bio cultures and their interactions (and who gave me some product after I begged for more as they no longer sell it in small amounts) I already knew two things - all alage in nature are vital links to sub and above species of plants and now learned that even this one is vital for instance in fixing nitrogen in Asian rice paddies where natural "forces" keep it in balance - something hard to replicate in our home systems.

I had already read (while just reading late at night) that this bacterial can release harmful and even fatal toxins.

So I continued... but to make it short to get back to your worries, turns out this occurred (as best my reasoning figures after days and nights of research.)

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FACTORS

PH extremely acid... for who knows how long but figure a while.

This acid water had a negative bearing on the water chemistry. (water chemistry can get real complex, ie redox and all - makes my head spin even though I have a background in biochemistry, and chemistry in advanced arts! lol)

Moss on bottom of sand (thought great will absorb gasses there, big mistake) forgot to say, my research yielded an exact experience by someone (experienced forums, not ask yahoo btw, lol) whereby corries being bottom dwellers can be the first to be affected by water quality at the bottom and pockets of moss there may be adding to the problem and low ph changes the chemistry of ammonia (et al) to higher toxicity then at higher ph levels.

This gets complicated but I figured it is a main reason this algae is often seen in photos of aquariums (on formus where I researched) along the bottom, its ability to migrate PLUS its unique ability to ......

Cyanobacteria are the only group of organisms that are able to reduce nitrogen and carbon in aerobic conditions, a fact that may be responsible for their evolutionary and ecological success. The water-oxidizing photosynthesis is accomplished by coupling the activity of photosystem (PS) II and I (Z-scheme). In anaerobic conditions, they are also able to use only PS I cyclic photophosphorylation  with electron donors other than water (hydrogen sulfide, thiosulphate, or even molecular hydrogen) just like purple photosynthetic bacteria. Furthermore, they share an archaeal property, the ability to reduce elemental sulfur by anaerobic respiration in the dark. Their photosynthetic electron transport shares the same compartment as the components of respiratory electron transport. Actually, their plasma membrane contains only components of the respiratory chain, while the thylakoid membrane hosts both respiratory and photosynthetic electron transport.

http://en.wikipedia.org/wiki/Cyanobacteria

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(I normally link the research to all this but saving time here). Any way, I had been waiting to get a much larger filter (have several smaller) but had figured wrong about them circulating the bottom areas (so I figured) and put in a canister at the bottom to circulate the water.

Moss not growing back (did so rapidly after a trim, so rapid each week I had to trim several inches - now it was stalled, and java leaves wilted?

Minus in water chemistry, and reason (not sure why exactly) it's growth was stunted even though it is said it can grow in a wide ph range?

Cyanobacteria.... (but not in betta bowl - huge in living room - cooler much cooler with same moss and same needle leaf java ferns, no wilt, no blue algae.)

One week of high heat due to NYC heat wave (finaly put fan to direct other room ac to help) Over 100 degrees plus.

(this class of algae is complicated but basically during rise in temperatures it can dominate!)

Blooms usualy occur during hte warmest months of the year, esp when the water contains an over abundance of nitrogen and phosphorus.

As well, grows with increase of PHOSPHATES which as well lower ph (and which is added to muncipal water supplies (along with much else) to curb bacterial and other growth during warmer seasons (I did much research on this area, but all the dots were starting to connect - man good thing I studied sewage systems in my Oregon degree (first in pre vet/zoo/ocean sciences and we studied NYC sewage systems for some reason! lol)

I checked this and yes, confimed this research.

Excessive P most often provides the stimulus for cyanobacterial blooms... esp if the total N to total P concentration ratio is less then 10.

Great link among many.

http://www.envirologix.com/library/KU_Manuscript_Toxic_Algae.pdf

And importantly, it releases cyto toxins!

Certain cyanobacteria produce cyanotoxins including anatoxin-a, anatoxin-as, aplysiatoxin, cylindrospermopsin, domoic acid, microcystin LR, nodularin R (from Nodularia), or saxitoxin. Sometimes a mass-reproduction of cyanobacteria results in algal blooms.
These toxins can be neurotoxins, hepatotoxins, cytotoxins, and endotoxins, and can be dangerous to animals and humans. Several cases of human poisoning have been documented but a lack of knowledge prevents an accurate assessment of the risks.[19][20

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My conclusion (believe me tons of research to get there but had done much before and was directed by this)... and more importanly solution.

A confluence of factors (think many were building, heat was tipping point) were involved to basically allow aglae (cyanobacterial) to grow for first time, and released neuro toxins causing my boys to die and the in ability to swim correctly (I had seen true whirling disease in fish and ruled it out (one is never sure though with no real tests done).

Build up of sulphr, nitrogen and other gasses in those pockets of moss growing along the bottom areas in stagnet low water circulation.... like a swamp.

(this is my assumption as I did not test it but enough researh convinced me - I have many links have to go back and read them again)

Heat wave caused wilting of needle leaf java ferns, and stunting of growth (thought it would die actually) as it does not like excessive temperatures and I am sure the tanks were hot...even with fans.

Most importantly, when I removed the fish and started slow water changes along with meds (may not have been necessary but it is bacterial and gram negative at that ie the CB)...

they almost immediate improved and most importantly, the one exhibiting signs of brain functioning damge is now acting normally.

(huge changes to tank, new 75 filter, with length of intake all the way to bottom of tank, another filter to the right side (was there before but legnthed the intake to bottom to increase circulation).... Canister still there at bottom solely to have a nice flow all the way to other side of tank (creating nice undulations of sand and cories love to ride the "wave" up and down these sand peaks, lol).

I removed all wood and soaked in Erythromycin which kills this bacteria as researh shows and IT DID... now fine brown filiments amongst the moss which is growing back in...

as well, the algae (CB) can dominate other forms of plant life if conditions are right, so may be another reason moss was not doing well in addition to heat?

Turns out the treatment I chose (minocycline) as well does the following - helps stop neurological damge: (now this is a human study, but I knew with a degree in psychology (year one brain chemistry basically) and mom a nurse in private practice for neurosurgeons (read all those books in high school on up) so I knew that many fish diseases (and other animal species) are one and the same (or similar) and manifest different, and that all fish meds are trickle down from people meds... (as well as art's materials/chemicals.)

So maybe this choice as well saved the poor guys brain from further damage.

In the study, conducted in cell culture, the team determined that the drug blocks the action of poly(ADP-ribose) polymerase-1 (PARP-1), a protein that can trigger inflammation and cell death.

The way in which minocycline works has been very unclear until now, says principal investigator Raymond A. Swanson, MD, chief of neurology and rehabilitation at SFVAMC. "Minocycline turns out to be an extraordinarily good PARP inhibitor, better than most of the drugs that are marketed as PARP inhibitors," he says..>>

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In conclusion:

Heat wave lasted one week, normal temps followed now cooler. City no longer has to watch for warm water fungses, water molds and bacteria so phophaste and other additives is down.

Phosphates can lower water ph... and this along with bottom stagnation drastically change water chemistry maybe only at bottom who knows, but created poisons.... corries first to notice since they are on bottom (even though our water comes through lime beds balance must have been thrown way off.)

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Cyanobacteria algae gone and no return.... (factors above and treatment)

Minocycline effective at lower ph (I got it to 7.0 in hospital tank ) and wish the muncipal water stayed low as now it's back to its old high... but guess since no trouble will take it, lol.

Now all is well, (whew) but it took several weeks for my moss to start growing as it had prior, needle leaf starting to send out new shoots, and corries (three that remain from original school of six - sorry guys - I feel terrible actually...) and will take it from here.

But major lesson learned... (maybe this is during change of season we shall see)

DO WATER CHECKS ONCE A WEEK OR A FEW WEEKS ALWAYS..

NEVER ASSUME

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LINKS

(much on this site)

http://americanaquariumproducts.com/Aquarium_Information.html

Unlike many aquatic websites, much of our research is outside the aquarium industry/hobby so as to not rely on common anecdotal assumptions (such as Redox). We also use aquaculture, horticulture, medical, lighting industry and university research papers to compile many of our articles.

His great article on Redox:

http://www.americanaquariumproducts.com/Redox_Potential.html

http://www.americanaquariumproducts.com/AquariumMedication2.html

Great info on water chemistry. (things often overlooked)

http://www.bestfish.com/oldtank.html

http://www.thekrib.com/Plants/CO2/caco3.html
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http://www.americanaquariumproducts.com/AquariumMedication2.html

Great link - he has a business, is experience and quick reference with links to serious research.....has mention of items not always found at other sites (unless one does the real reserch). (such as rendered ineffective at higher hardness/ph levels)

MINOCYCLINE:

USE: Minocycline hydrochloride, also known as Minocycline, is a member of the broad spectrum tetracycline antibiotics, and has a broader spectrum than the other members, especially as to gram negative bacteria. Minocycline is also synthetic whereas Tetracycline Hydrochloride and Oxytetracyline are naturally occurring. It should also be noted that Minocycline maintains serum levels 2-4 times that of most other tetracyclines (150 mg giving 16 times the activity levels compared to 250 mg of Tetracycline Hydrochloride at 24-48 hours).

It has excellent anti-inflammatory properties which makes it a good choice for septicemia, although for Viral Septicemia there is no effective treatment, only prevention. Minocycline is also effective for fin/tail rot and OCCASIONALLY pop eye and is sometimes suggested for dropsy. However as for Dropsy I strongly recommend against this as this antibiotic can cause severe kidney damage, which is the last thing you want with a possible Dropsy case. For more about Dropsy, please see this article: Betta with Dropsy

Minocycline is also skin absorbed like Kanamycin (although not as well) which can increase effectiveness. It is also nontoxic to invertebrates but should not be used in Marine aquaria.

Another note about the dangers of Minocycline as with Tetracycline, it becomes dangerous past its expiration date. Minocycline can more toxic over time.

Minocycline (like other Tetracyclines) is easily absorbed by calcium, making this a poor choice for saltwater or high GH freshwater aquariums (such as African Cichlids, livebearers), in these cases Kanamycin is the better choice.

The above point is often missed by well meaning aquarists (often in many forums that love to recommend Maracyn-2), Maracyn ÂTwo (Minocycline) is a good product when used in the right conditions for the right problem (of which it is relatively wide spectrum), the problem is that most aquariums I have either encountered or have read the water parameters for have too high of minerals (GH over 200) for Minocycline to be truly effective, in fact there in lies the problem in that often these minerals that render Maracyn Two less effective IMPROVE the fish natural ability to fight disease.

With these points in mind, generally the ONLY aquaria I recommend Minocycline in are Amazon River tanks such as Discus Aquariums.

DOSAGE: Maracyn-Two is the primary source for this anti-biotic, follow directions given by Mardel (manufacturer of Maracyn Â2)

References: Minocycline Hydrochloride, PDF
Minocycline

Not called Maracyn - One (my own lable for it)

There are two Mardel products with Maracyn in the name - one is Maracyn which has Erythromycin in it (one for algae/bacteria) the other is Maracyn-Two Minocycline. I posted it in my earlier email as Maracyn - One but it is just as others mentioned - Maracyn (looking at both boxes now, with lights on, lol)

Good luck, Sherry

There is only one permanent fix to this problem. Sufficient aeration of the water.
The ONLY time EVER that I've seen green slime algae become a problem in ANY tank regardless of water quality is when there is not enough dissolved oxygen in the water. With sufficient aeration, it goes away completely on it's own.
It makes sense, cyanobacteria require a low-oxygen environment to live. If anyone has a bead on another common and plausible cause, I'd be interested to hear it. But I've never encountered it before. The advice online is good... water quality... etc... etc. But when I see it, I'll believe it.
The fish seem to survive just fine in these low-oxygen tanks covered in green slime, but mine seemed much more lively once I fixed the problem.

that is correct. However it does take time to reach that equilibrium. I eventually corrected the problem by introducing aerating plants.