Re: Floating algae

[Thomas Barr <tcbiii at earthlink_net>]

> From: "Loh Koah Fong" <kfloh at ntu_edu.sg>
> Subject: help with this algae/ scum on the surface
> 
> Hi,
> 
> Some time back, I noticed some kind of greenish powder on the surface of my
> 4ft tank. Covering maybe 60% of the surface. No smell. See the picture of the
> algae at http://www.ntu.edu.sg/home/kfloh/photos/what_algae.jpg

It's a cynobacteria. These float particularly well.
You can dab it up using a paper towel.
Some surface movement can also entrain it down in the water in some mild
cases often killing it off.

> 
> It caused my fish to go to the surface in the morning as if lacking of oxygen.

Well it does not, but your lack of surface movement does and lack of O2
production from your plants. Add some current to your tank.
 
> It has wiped out my entire stock of 20+ Harlequin Rasbora and some Cardinals.
> Before they die they are swimming weakly and haphazardly near the surface. The
> scum seem to be concentrated at a corner of the tank above my E. bleheri which
> has some leaves growing out of the water. The water is quite stagnant over
> there.

Well add some current. No current=> no exchange of nutrients for the plants,
=> lower O2 production of plants etc. You've taken the reduced amount of
surface movement too far. This is a physical, not biological issue.
Increasing plant growth will add more 02 also.
 
 
> The tank was set up 2 years ago and nothing significant was done lately.
> Currently I am using DIY CO2 which I run it through a reactor non-stop. It has
> not cause problems before. And I am using a skimmer to remove the scum weekly.
> 
> I wonder how it originates and how to remove it?

No current and low nutrients. Add some current, add emnough nutrients for
your plants to produce more 02.
Regards, 
Tom Barr
> 
> Thanks for any help.