Does lowering phosphates mean the death of my cyanobacteria?

[Nathan]

I have pretty low phosphates (less than 0.03), but I still have tons of cyano! I run an iron-based phosphate media in a phosban reactor and I can tell that my levels are low because of Salifert test kit and because it takes days for the green film of microalgae to build up on the glass.

But I have prolific cyanobacteria despite this.

I had been dosing Sodium Nitrate for my seaweeds (macro algae), but when I test my Nitrates (Salifert) it is BARELY detectable.

So... other than using Chemi-clean, how would I get rid of cyano? I vacuumed it out and one week later it was back in full force.

-Nathan

 

[Amphiprion]

Without an abundance of PO4 in the water, the next culprit is detritus. It seems to settle on any detritus quickly, since it is a good source of PO4. Be sure circulation is good and try to eliminate dead spots and detritus deposits as much as possible. Be aware that this is all cyano needs to thrive.

 

[Nathan]

Ah ok. So can cyanobacteria survive with no nitrate? I'm just thinking that maybe there is some limiting nutrient.

I have a 180g tank with 2800gph split between two sea-Swirls. I do notice that my cyano grows in some spots and not in others... but it also does grow in high flow areas too (the currents are strong on the sand near the front glass)... so I am not convinced that it's all about the detritus or even flow. I feed my fish very little (once or twice a week) and I wouldn't imagine that there would be much detritus there...

-Nathan

 

[Amphiprion]

Right. You mentioned in a separate post that they "fix" atmospheric nitrogen--which is entirely correct. With this source of N, they have no need for dissolved nitrogen.

 

[Nathan]

Amphiprion,

You are correct! Check out what I just found:

http://www.ucmp.berkeley.edu/bacteria/cyanolh.html

Cyanobacteria are very important organisms for the health and growth of many plants. They are one of very few groups of organisms that can convert inert atmospheric nitrogen into an organic form, such as nitrate or ammonia.

SOOOO!!! They MANUFACTURE nitrate and/or ammonia! Ok, I had it backwards in my mind. I thought that it was converting nitrate to nitrogen gas!

So how do I starve my cyanobacteria? (I can't do much about detritus). Also, wouldn't "more flow" = "more nitrogen rich water"?

-Nathan

 

[Amphiprion]

To an extent, but if you limit the places for detritus to settle, you wont have as much of a problem. Besides, there is vastly more nitrogen in the atmosphere than oxygen, anyway, so you can't avoid that.

 

[Nathan]

Is freshwater cyanobacteria the same as saltwater cyanobacteria?

 

[Habib]

Cyano in aquaria will thrive if ammonia (but also nitrite or nitrate)and phosphate are high.

If the inorganic phosphate is low (the form detected by phosphate test kits) then they can still thrive on organic phosphates.


Are the macroalgae growing fast? If not you might want to try supplementing with iron. The Macroalgae should be able to compete for the same nutrients the cyano require.

 

[Nathan]

My macroalgae is rather slow growing.

I have a PolyFilter. Will this remove the chleated iron that I add? (ie, should I remove my PolyFilter?)

-Nathan

 

[sjm817]

What is your alk reading? IME, Cyano likes low alk. Raise it up to 9 - 10 and it will not thrive.

 

[Amphiprion]

<a href=showthread.php?s=&postid=6977640#post6977640 target=_blank>Originally posted</a> by Habib
Cyano in aquaria will thrive if ammonia (but also nitrite or nitrate)and phosphate are high.

If the inorganic phosphate is low (the form detected by phosphate test kits) then they can still thrive on organic phosphates.


Are the macroalgae growing fast? If not you might want to try supplementing with iron. The Macroalgae should be able to compete for the same nutrients the cyano require.

Let me clear what I said up a bit, as Habib is also correct. In the absence of adequate amount of dissolved nitrogenous compounds, cyano can still live and do quite well, as long as phosphate is available (due to fixation). But if these nitrogenous compounds are available to the bacteria, it also takes less energy to utilize them instead of fixing the nitrogen--so in other words, if it is there, they will use it first. I never meant to imply that they will not utilize it, only that they don't NEED it, per se.

 

[Nathan]

sjm817,

I have 3.2meq/l (9dKH). I am going to try raising my alk to about 3.8meq/l (10.64dKH) and see what happens.

Amphiprion,

I think I get what you are saying. But I did need to re-read that several times.

-Nathan

 

[Habib]

<a href=showthread.php?s=&postid=6977682#post6977682 target=_blank>Originally posted</a> by Nathan
My macroalgae is rather slow growing.

I have a PolyFilter. Will this remove the chleated iron that I add? (ie, should I remove my PolyFilter?)

-Nathan

I don't think that the polyfilter will remove iron if the concentration is not higher than a few ppm. That concentration is still high enough for the macroalgae.

 

[Nathan]

Habib,

Thanks.

Here's another thought:

What if the phosphates are "living" in my sand some how (since the sand is the only place where I see cyanobacteria).

-Nathan

 

[Nathan]

Habib,

Does iron-based phosphate media (Phosban etc.) remove organic phosphates? Because I run iron oxide hydroxide in a phosban reactor. It does seem to control the microalgae that attaches on the glass and makes it green, but it doesn't seem to control the cyano -- but the cyano may be pulling phosphates out of the sand maybe...

-Nathan

 

[Habib]

I would not dare to say that all iron based phosphate removers would remove organic phosphates but at least some will do so.

Decaying matter in the sandbed could be a source but could also be the water. If the cyano outcompetes the algae then reduced algae growth on the glass would be observed.

 

[The Reefer91]

i wouldn't neccesarily blame the sand. alot of things can make cyano algae. low flow, organic and non-organic PO4, nitrate, ammonia, Cocoa puffs(j/k) the point is, there may be alot of causes(helpful, i know ) your best bet is to take out every possible thing it could grow of of.

that or you could give me your fish tank and i'll take care of it