Blue/green algae: a possible cause

Our 10gallon community tank has been going on perfectly happily for
several years. Then in the last year we have been battling blue/green
algae. Now my best understanding is that this is usually a symptom of
too much phosphate. So where has this phosphate suddenly come from? I
have begun to ask myself. It must be something I am adding to the tank.
About 18months ago I switched from flake food to Tetra Prima, the orange
granular stuff. Largely because we have no surface feeders anymore, just
scissortails and tetras in the midwater.

Now a perusal of the ingredients reveals L-ascorbyl-2-polyphosphate,
obviously a VitC derivative which is almost certainly in there as a
preservative. Both the Tetra algae wafers and tabimin food for the
bottom feeders have it too. IIRC we swapped from a Japanese algae wafer
to the Tetra stuff too. So there I seem to have a cause.

We have an air driven ugf (works just fine for us) so removal with ion
exchange resin is not practicable. So I am trying to dilute it out,
which will not work unless I change the food I have now realised (they
have been eating frozen the last 2 days).

Any comments, suggestions?

Peter

--
Add my middle initial to email me. It has become attached to a country
www.the-brights.net