Plants Dying!

[MP]

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

[Pete]

"MP" > wrote in
:

> 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
>

How often have you been doing water changes? If you have been having
plants growing like gangbusters and haven't been doing any water changes
until the last one, you could have easily used up other nutrients.
Here's a link to a list of deficiencies and what they look like.
Read down past the chart to the large written descriptions (it's the best)

http://www.thekrib.com/Plants/Fertilizer/nutrient-deficiency.html

I've got water lettuce which is much larger version of duckweed (nice for
your tank if you can find some) and it had a similar problem where the
older leaves just seem to dissolve from the outside in (older leaves
first). It was a potassium deficiency with me.

High phosphates shouldn't damage your plants. But for where it comes from
check your tap water for phosphates, you might be starting off high.
Otherwise you can get it from excess food (usually have to be pretty bad),
cheap charcoal, PH buffers...

If you haven't been changing your water until now, you might have just
fixed your problem with your water change (getting rid of some phosphate
and adding potassium etc.). If your plants perk up just try weekly or
every other week water changes.

Luck
Pete.