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[APD] RE: Oedogonium & black-outs

"Background for Dr Armstrong's reference: We are discussing control of
Oedogonium epiphytic filamentous algae infecting a 5 yr old 75 gal
aquarium with 250 watts MH lighting, moderate fish load, CO2 injection 1
bubble/sec, regular water changes with CA, K, NO3, Mg & trace
supplementation. P is provided primarily via fish food/wastes and from
soil in pots."

Well soil has a limited amount after 5 years don't you think? Morderate fish loads are not going supply enough PO4 from waste. They have higher amounts of N relative to P for sustained growth.
Plants will do "okay" with PO4 limitation, but PO4 limitation does not limit algae in any way in this case or most anyone's aquarium. You have to get down to ppb and most Phycologist have trouble seeing what ranges will limit algae and periphyton, see South Florida water district water quality mandates(10ppb PO4 effulent), they have trouble even measuring this in a lab being very careful when you consider error. Periphyton grows fine. Also some work done by Ulrich. There are methods to do this, but they are very troublesome much like Fe limiting studies. PITA and I'm glad I don't do these. 

Adding PO4 will drive NO3 uptake and also NH4 uptake perhaps 2-5x faster. 

"There is an abundance of CO2, nitrate and other minerals. No shortages

IME, 90% of all algae issues are derived from low or variations with CO2 if you keep the other issues/nutrients fairly constant. I check that even if I think I'm right and then I check it again. 
Check it over a daily(AM and PM times) and a weekly variation, not just once and that's it.

Don't try to deal with algae until you first address CO2 closely. 

 "The substrate is contained only within pots in this tank and is
over 5 years old in all cases."

Ask any nursey grower/wholesaler if they replant once every 5 years with small herbaceous plants in small pots.

"Oedogonium has been present in small
amounts for quite some time in this tank but what has apparently
triggered it is the increase in nitrate levels in the last 3 months."

See PO4 drives NO3 and NH4 uptake. NO3 by itself will not trigger this alga up to 75ppm(or any others after 3 weeks) with a densely planted CO2 enriched tank. 

"Other tanks which are showing tremendous growth improvement with
increased CO2 & nitrate do not have this problem however the other tank
that has been exposed to Oedogonium has a lot of Rainbows in it and they
might be eating it. The other difference between the tanks is that the
problem tank has a lot of slow growing plants in it. I have a huge mass
of H polysperma in this tank which grows very rapidly and I crop it
regularly for sale. The slow growing plants cannot throw out leaves fast
enough to keep ahead of the spread of Oedogonium. The new growth on the
H polysperma does not appear to have any colonization by Oedogonium
(yet). I do not have a microscope nor access to a microscope so I cannot
determine if there are any small colonies on the H poly. There are a lot
of assorted Tetras and Sword tails in this tank; not exactly the best
algae grazers. I might be able to get a hold of some Mollies which are
said to be good grazers."

Well, based on what you have said here: You are likely on a very close line limiting the PO4, one tank has just barely enough while the other likely does not have enough to support the growth except with the fastest grower(H polysperma) and you are seeing plant-plant competition occuring as a result and very low PO4 levels.
When the PO4 is limited in this case, NH4 uptake will also slow as will NO3 uptake. 
The other tanks might have a enough PO4 to keep ahead of the algae.
The NH4 is only required for perhaps a 24-36 hours to induce a bloom so a slump in a critical plant nuterint could signal a bloom for several algae species, green water, Staghorn, this alga etc are all inducible with NH4.

When talking about algae absense/presense, you must address the forms of nitrogen(NH4, NO2 or NO3). 
You can also do a similar experiment with DOP and DON vs DIN and DIP.

"So I submit that the reason I have it is not due to a lack of nutrient
dosing. Perhaps with a different population of fish or a bigger
assortment of fast growing plants, this tank would not have a problem.
Slow growing plants do not seem able to out compete filament algae when
you start to push the nutrients. I think the green filament algae groups
(Oedogonium, Cladophora, Spirogyra) really gets going well when you
provide "ideal" hydroponic growing conditions for aquatic plants."

They grow when your plants don't. 
Learn that and you will not have algae issues. 
It's that simple.
As far as why algae grows, that's another topic.

"I do attempt to prevent infestation of my new aquariums by the use of
the bleach protocol (ala Krombholz). Spirogyra seems to spread from tank
to tank very easily however it is the easiest to combat using the
black-out protocol that we discussed several months ago. Strangely,
Oedogonium does not seem to spread from tank to tank although I cannot
be certain that there aren't small colonies of it in some of the tanks.
Once it takes over, it can be a real problem to get rid of. I had a bad
case of Oedogonium several years ago and I resorted to tearing the tank
down and bleaching all the plants and equipment."
Oedogonium does have motile zoospores however the motile zoospores do
not seem to survive on equipment if you dry it off or rinse it off. That
is educated guess work."

Some larger macro greens can perhaps be prevented, I do not do this protocol and I gather plants that are infested quite often yet have no issues with any of these algae and I also have tanks with no herbviores at all.
SAE's are particularly useful herbivores IME for this alga that is giving you trouble.

"According to Paul K, in private emails, he has said that he has tried
very long blackouts with Oedogonium (6 months) and the algae did not
die. To me, that suggests that the algae had formed non-motile zygotes
(combination of a non-motile gamete egg and motile gamete sperm) which
can be dormant for extended periods. Oedogonium also produce asexual
motile mitospores which attach and form new filaments. These are not
dormant or persistent spores."


So there, try the air for keeping out the algae:-)
Bleach might keep some species out, but not this one. When the plants don't grow, the algae will.  

"So finally, my question:"


"Tom, have you ever used the black-out protocol to try to kill


" Do you think it will be successful in knocking down the
thick colonies that are covering virtually all the leaves of my slow
growing plants in the problem tank?"


"Steve Pushak
Steve's Aquatic Plant Resource Page"

Try less light, high CO2, good nutrients.
Use light rather than nutrients to slow growth, this works extremely well for slow  growth plants. 
It's a version of the NON CO2 approach in some respects and yields very good results, but 1.5w/gal -1.8w/gal is the range that seemed to work best for both the plants and less algae. 

There will be some variation based on light type/spread, tanks depth etc.

Tom Barr

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