Hi everyone ... we bought an aquarium for our school about 6 months ago and
everything's been going swimmingly until this last couple weeks. There were
duckweed growing crazy ... I kept thinning it out with a net ... and several
leafy plants growing anchored to the substrate. Then 2 weeks ago I noticed
the duckweed dying off ... and now they're virtually gone. One leafy plant
has died completely ... and the other has leaves that look like they're
rotting.

I did some water tests today ... pH was 7.2 ... nitrates, nitrites, hardness
were all "healthy" ... but the phosphates were off the colour chart. I did
a major water change ...

My question is: would extremely high phosphates be responsible for the
plant's deaths? What would cause the phosphates to get so high in the first
place? Is there anything to do besides changing water?

Thanks!

Mike