Cyanobacteria problem - Journal

In my zero maintenance plant tank experiment, I ran into a bit of a problem
that I'd like to document for everyone here.

This tank has been up and running now for 11 months with very few water
changes, and very little maintenance, plus no feeding.

Originally, I had and used my Duplaplant 24 drops on the tank to provide
iron supplementation, but added no additional fertilizer or fish food to
the tank.  This worked well while the tank had algae, but when the plants
caught up and overcame the algae, most of my fish and apple snails starved.

At roughly the same time my fish and snails started to decline, I noticed
nutrient deficiency syndromes in some plants.  I was still adding iron, so
I knew it wasn't that.  Some leaves were getting holes, and other new
leaves were turning yellow, so I suspected a Nitrogen and Potassium
limitation.  A month or so of this and I ran out of Duplaplant 24 also, so
I went looking for trace element mixes to get Duplaplant 24 up and going.

Apparently trace element mixes aren't easy to find in Dallas unless you're
willing to go to a head shop.  I'm not, so I located a pool and pond supply
store locally that sells 1 liter bottles of Pond Flourish.  Knowing that I
needed to do something quickly, I bought the Flourish and started using it
(should last me the next 30 years).

The Flourish fixed the holes in the leaves of my crypts, but not the
yellowing leaves of my anubias, and after another month or so, the anubias
started to melt.  They were both nearly 11" tall at the time (this is
barterii v. 'nana', btw) and lost most of their lower leaves.  This is also
when the cyanobacteria showed up in force.

I suspect that two things happened at the same time.  The iron
concentrations in my tank may have dipped below a critical level that was
keeping my phosphates in a precipitate state because my plants were
consuming iron.  I also suspect that the anubias had stored a huge amount
of phosphates in its leaves and when they melted, the phosphates were
released into the water.

At first I noticed a small cyanobacteria patch that had lived peacefully on
the floor of my sump started to get larger.  Within a month, cyanobacteria
was covering nearly every surface in my tank.  I was still adding Flourish,
but something was wrong.

I had noticed a while back that my snails were doing very poorly, and I
wanted them to do a lot better.  I also wanted to provide my plants with
whatever nutrients they seemed to be missing, so I went to a local farm
store and purchased 5 lb. bags of K2O and NH4S04, plus a half pound of

After doing a little testing with the NH4SO4 to determine what would be a
safe amount to add to my tank, I began adding a daily dose of 10 grains.  I
also added a one-time teaspoon of CaCO3 to the tank, and continued with the
In addition, I removed my H. difformis and some of the valisneria (the rest
goes later), and moved some of my Lilaeopsis brasiliensis and some crypts
to an emersed spot on top of a mass of R. rotundifolia just to make sure I
didn't lose them to the reduced lighting.  The crypts will eventually
replace my Rotala and althernathera stands.  Finally, I saw a few trumpet
snails in the plant tanks at the aquarium store last week, so I got them to
give me a few to add to my tank, and I also purchased some blackworms to
see if I could add some biodiversity to my substrate.

Result:  The snail population in the tank is growing exponentially (not the
trumpet snails yet) and they are slowly making headway against the
cyanobacteria (no word on the blackworms yet).  My anubias is growing
rapidly again, with healthy, green leaves.  My Rotala rotundifolia, C.
wendtii, Hydrocotyle leucocephala, and H. polysperma are poking up above
the water level for the first time, and my Alternathera reineckii is
perking up again.  

The algae's not gone, but the tank is looking better.  

I know that I'll need to increase my water change interval now that I'm
adding sulphates to the tank.

I haven't opened the K2O yet, and don't know of how to test for potassium
levels in the water.  What effect should I expect from adding K2O to water?
I'm looking for something measureable, like maybe a pH swing or something.


David W. Webb           Enterprise Computing
Texas Instruments Inc.  Dallas, TX USA
(972) 575-3443 (voice)  MSGID:       DAWB
(972) 575-4853 (fax)    Internet:    dwebb at ti_com
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