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Re: Aquatic Plants Digest V1 #20

In reply to:

> From: Matt Rhoten <mrhoten at oz_net>
> Subject: Strange water values, hypothesis

Hmm ... what have you added to your tank lately that may have increased
phosphates?  Any buffers?  My own experience with overfeeding a tank lately
to provide nitrates has not increased phosphates - that's using Tetra flakes
though & other foods may contain more phosphates, I think live foods do.

When I've added phosphates (in Plant Tabbs), I've found that the plants are
very slow to remove them, especially compared to nitrates.  My nitrates will
drop from 20 ppm to 3 ppm within a week, but phosphates take several weeks
to drop from 1.6 to 0.8.  If I decide to increase nitrates nowadays I use
straight KNO3.  I figure if my plants have been sucking the nitrates out
of the water then they need extra nitrogen.  I overfeed also!

I would not worry about your phosphates too much unless they keep increasing
(above 2 ppm I'd worry) and/or you see too much algae growth.  Adding CO2
should help the plants outcompete the algae.  I'd put a DIY unit on now if
I was you - it's easy!  But I'd also try to figure out the source of your
phosphates.  If it's your tap water then you might want to use distilled
or RO water for a while - it may just be a seasonal thing, e.g. recent rains
washing fertilizers into the water supply?  Try calling your local water
supply company to see if they can tell you if phosphates have increased lately
& if it's a yearly trend (& likely to decrease soon).

> My plan of attack for the short term is to reduce the lighting for a
> while, aerate the water more (to get CO2 _into_ the water, of all
> things) and, God forbid, feed more heavily.

I'm not sure if reducing lighting would be such a great idea since this may
allow the algae to get a foot hold with the phosphates present.  Aerating
the water will *not* get more CO2 into the water.  A DIY CO2 unit (just a
teaspoon of yeast, 1/2 cup of sugar + some water in an old soda bottle with
a hole drilled in the cap for an air(CO2)line running into the tank) is your
best bet IMHO.  Be careful about feeding more heavily - check your food for
phosphate level if possible or monitor phosphates & make sure they don't
rise.  Perhaps switch to another food brand.

> add sodium bicarbonate to keep my carbonate hardness up and my pH
> stable

I don't think this is a good idea.  Sodium bicarbonate will also raise the
pH, not stabilize it.  Again, DIY CO2 is your best bet IMHO.

Joanne.