water values [Re: Aquatic Plants Digest V1 #14]

Allen Sandifer writes:
>[Karen Randall writes]
>>I suspect the high phosphate reading has another source.  Have you 
>>added any potted plants without removing the rockwool?  Any new 
>>water conditioners? pH adjustors? fertilizers? In my experience, 
>>when phosphate goes up in the absence of high nitrate readings, it 
>>is usually being added to the system inadvertently.

>I had no idea that rockwool would add phosphate to the water. I am glad that
>you mentioned this, there are times when I get plants and just stick the
>little pot rockwool and all in the substrate. In fact I have a couple in the
>tank now. This could be a contributing factor to my small alage outbreak.

I don't have any potted plants, and the only thing I can figure out
that changed about the tank lately is its temperature. There must be
some factor I'm missing, but I don't know what. In the meanwhile I
will fight the phosphate with aggressive water changing / gravel
vacuuming. Who knows, perhaps there's some area of gravel with mulm
steadily rotting away into ions.

It is very interesting indeed about rockwool.

Erik Ostrom writes:
[wrt me suspecting plants are blocked on CO2]
> Check your pH AT NIGHT, and see if it's dropped down to 7.0-7.2 when the 
> plants aren't using it; this will confirm your suspicion.

On Erik's suggestion I tested pH at various times last night; the pH
did indeed swing down from 7.6 to 7.3-7.4. Looks like it's time to
wander by the welding supply place!

On the good side of this problem, I am moving soon, so will have a
chance to fix up a few things at the time of moving. For instance, I
will replace my rather large gravel with blasting sand, get some
better ion supply into the substrate, and so on.