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Re: PO4; organic vs inorganic

> From: Luca Specchio <lucky_luca at mclink_it>
> Subject: PO4 dosing and timing
> Hi folks,
> I know that some of you dose regularly some PO4 in your tanks, I'd like to
> ask you which is the quantity (daily dosage) you add , and when it's
> preferable to add it? during light period or during night?
> thanks! :-)
> Luca

I think it's not too much of an issue when you add the PO4. As far as
dosing, 2-3 times a week is fine if you have low PO4 or high PO4 usage
rates. If you have been low on PO4 for sometime and add .3ppm it will be
gone very quickly(less than a day).
Perhaps the best PO4 source is KH2PO4 since it also supplies the K and is
cheap. This is the standard I use for this.

As far as an amount each time? Well that would depend on your target level.
Some want to try to stay at .2ppm (I don't think that's the best approach)
some want to stay at .5ppm, some 1.0ppm some even higher. I see little gain
to go beyond 1.2ppm or so. I also do not see algae beyond 1.6ppm or so.
But this addition can go sour rather fast if your CO2 is poor or if you have
high NO3's etc.
You can test your tank directly by adding tiny amounts and test(within 10-20
minutes). You can add it by taking a certain amount(let's say the size of a
pea) by certain water volume to yield a ppm range. A 1/2 a Pea's worth is
enough for a 75 gallon(284 liter tank) added 2x to 3 x a week.

It's worth noting that organic bound PO4 may be also tested. Whether this is
available to the plants more than the algae is another issue. Plants do
prefer inorganic forms of NO3 and PO4 from what I've read. How fastb the
tank cycles between breaking down the organic forms into their organic forms
plays some role.
What's that mean? Well a big filter may help a lot. Your test kit may tell
you that you have lots of PO4 but much less is available to the plants than
you think there is (giving you high PO4 readings). NO3 may break down from
one form to another much faster than PO4. Maybe not. But it might......I'll
stick with adding inorganic to keep things simple.
Tom Barr