Re: orthophosphate

[Thomas Barr <tcbiii at earthlink_net>]

> He said that my water should have:
> Nitrate: < 0.28 mg/l
> Iron: < 0.1 mg/l
> Zinc orthophosphate: they maintain a level around 0.45 mg/l (measured as
> orthophosphate)
> 
> I did an archive search on "orthophosphate" and came up with this
> reference from 1996:
> " Yes, water systems do add orthophosphate to control
> corrosion in the water system.  Yes, the phosphate will
> 'tie-up' the iron fertilizer and make it useless.  The more
> major problem from the phosphate is that algae loves
> phosphate and will grow like crazy.  Even at the low levels
> used by water systems of 2mg/l (ppm).
> Some water systems use Zinc Orthophosphate which will
> increase the amount of zinc ions in the water.  Zinc is more
> of a problem in salt water aquaria."

2ppm is pretty high for a utility to use or need.

Orthophosphate is available PO4, not bound etc. It's the most available form
to both plants and algae.
Zinc I've used in excess for some time and plays little role I can see in
aquarium. I have not gone through to any great depth, but it appears to be a
minor player as far as I can tell. I would not worry much about it. I've had
very high levels due to galvanized zinc metal coatings in some tanks.

As far as tying up iron or more like tying up PO4, I think this plays a
pretty minor role and there's little way around it.
We need both in solution to get the best plant growth. There are various
binders, eg Fe ETDA, Fe gluconate. How exactly this affects the iron/PO4
relationship I'm not certain. I do know what the plants like and use and
follow their lead as an indicator. So I certainly can say "this is how....

Your tap water sound great on the N, assume it to be 1ppm or so. Tap water's
PO4 is actually a little low even if you did 50% weekly water changes, you'd
only give enough PO4 even at 2w/gal for about 1 day's worth of PO4 plant
uptake.
PO4 doesn't not cause algae in high density planted tanks with good CO2
levels, NO3 and other nutrients etc. You can prove this to yourself.

I've added up to 1.8 -2ppm of PO4, I don't have ANY algae. I used KH2PO4.
This dissociates and is in the orthophosphate form.
I've measured more than 0.2ppm consistently used per day of PO4 in tanks
over a number of years. Many tanks will use this much in a few hours.
I keep about .5 to 1.0ppm most all the time in all my tanks. I do weekly 50%
water changes and replace the old water with fresh nutrients and dose these
nutriewnts every 3 days or so. Nothing builds up either way.

You can also observe virtually immediate plant responses and algal declines
as a result of adding PO4. If a large amount if being bound we'd see less
plant response and much slower response.

Do a 50% weekly water change and note the tank's clarity and pearling.
If you add KNO3 and Traces, and have good CO2, the tank should pearl like
made for 1-2 days and then taper off.
NO3 uptake right before the water change will be slower, then for 1-2 days
it will increase, then taper off till you add more PO4 in the tank.

If the plants are not growing well, the algae will. Good plant growth= bad
algae growth.

 
> So, I guess I have two questions. Is it true that the orthophosphate
> ties up the iron? And do I have to worry about that at the level that is
> in my water? 

Yes and No. It can bind with PO4 but it's not a huge effect IME. Iron's
funny enough without worrying about PO4 which you need a great deal more of
anyway. It takes time for this to happen also. If the plant doesn't get it
in the water column, it'll get it out of the substrate.
 
> I'm having a nasty green water problem in my 38 gallon (finally ordered
> a diatom filter) and I'm trying to figure out what is going on.

One of two things basically, either not enough plant growth(Not enough CO2,
NO3 etc, or a spike, although a small one will do of NH4)
If you have a tank that produces say 1mg/l of NH4 a day and you never
measure any present due to ACTIVE HEALTHY plants, then there's no problem,
but if the plants are limited, say by PO4, then the rate of uptake for NH4,
NO3 etc declines.
GW is impossible to beat through nutrient limitation, you'll kill the plants
first. GW need next to nothing to grow. I'm talking like less than 0.0003ppm
of PO4.......no one has a testing procedure or kits that is even close nor
accurate enough to do this.

Once you kill/filter it, making sure there's enough NO3(Not NH4), K, PO4,
Traces and most importantly CO2 will prevent any algae from coming back.
Anything that slows down N uptake is bad. Healthy plants are your best
defense against all algae. So grow the plants and cater to their needs.

Regards, 
Tom Barr