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Re: Aquatic Plants Digest V6 #209

> The Problem
> A month ago I had a serious diatom "brown algae"
> outbreak in both my tanks and pond, which I traced to
> a high Phosphate, silicate and /or organic content in
> the source well water. I introduced a phosphate
> removing resin to the filter of the display tank. The
> Phosphate dropped from over 3ppm to less than 1ppm.
> The growth rate of the algal film diminished but did
> not stop, even with 13 otos munching happily away at
> it! The resin was specific to phosphate, so the
> soluble silicate (which diatoms incorporate in their
> cell wall) was still there. 'Not more resins!'  I
> thought.

It's unlikely you can beat diatoms with Si removers, they can live in very
pure water and are often found in such locations.
PO4 has been shown here and numerous other research studies that it does not
cause algae outbreaks __when growing plants__ are present.

The organic content.........well if it's got NH4 by products or high
Nitrogen generally, you have found the source of the tap water problem.
Running/adding carbon etc will help this.

 Too expensive for every water change. So
> after some light research into methods of removing
> Phosphates and Silicates I found that soluble iron
> compounds (ferrous sulphate, ferric chloride) are
> commonly employed to remove both Phosphates and
> Silicates  in water treatment plants. Well why not in
> aquariums?

Because PO4 is not a problem nor is Si. It's good for large scale pond/lake
issues, but you need to know if using this will reduce the algae/increase
clarity in the particular specific lake/pond you are treating.

Initially the water in most lakes/ponds/tanks even will clear. Whether it
stays that way can depend on many things.

Resuspension of that PO4/Fe from a reductive substrate will cause a bloom if
the water is PO4 or Fe limited which is likely the case if it cleared the
problem up over the long term AND if there are no plants growing well in the
tank/pond/lake. Adding PO4/Fe etc to a densely planted lake/pond/tank will
cause algae, the plants will grow more, but if there's around 50% coverage
on the lake, maybe more on smaller systems, you should not see algae

But if the tank is NO3 limited etc, nothing will happen.

NO3 levels vary so that can be different depending on your dosing routines
> The other benefits
> Ferric phosphate  which had fallen into the spaces
> between the gravel is probably acting as a slow
> release fertiliser. Phosphates are at the root zone
> where most needed . The ferric iron in the anaerobic
> environment is also reduced back to the ferrous  state
> which is theoretically more available.

So what happens when you uproot a plant? What happens to all that mulm?
Plants will take in PO4 rapidly from the water column, this can be measured.

I doubt there's much "preference" as long as there's enough PO4.

> New leaves are
> a nice rich green colour.
> The snails appeared to have stopped laying eggs.
> Possibly the fact that Ferric phosphate is used as a
> commercial molluscicide may have something to do with
> this.

In very concentrated form it is, but diluted down, it might not be the

Tom Barr

> Stephan
> Malta