Anonymous One wrote:

My wife and I have a very unusual situation. A plastic bottle of a
"Cactus Food" tipped over and sat in the solution for a day or so.
It is a slightly low spot of our concrete patio so it did not
evaporate as quickly as it might have on an area that did not "pond."
The solution is comprised of the following ingredients:

1.0% Nitrate Nitrogen
7% Available Phosphate (P 2 0 5)
6.0% Soluble Potash (K20)
1.0% Calcium

Derived from: Ammonium Nitrate, Calcium Nitrate, and Potassium
Phosphate.

What has happened is that it has stained our concrete patio, and
where the bottle had layed down, it has etched a groove in the
surface of about 1/2" or so. When we called the company they took no
responsibility, in fact they were rude, saying that this had never
happened before and it was impossible. My wife talked with someone
in a concrete manufacturing company who said this type of solution
could damage concrete. I did not know where to turn so I am curious
about what you folks in the chemistry community might think of this.
Also, it is odd. Since this has happened, every morning the area
where the spilled occurred appears wet, even though it is not
currently raining. It almost looks like moisture is being leeched
out of the air and drawn towards this spot? The person in the company
did tell my wife to drench the area with bleach, but that did not
help at all. Any idea, suggestions, etc. would be greatly
appreciated. We do not even know who to ask to help us as we do not
want the concrete to degrade now that it has been deeply etched.
Thanks in advance for any help you folks can offer.

Ammonium Nitrate, Calcium Nitrate, and Potassium Phosphate are all
nicely reactive compounds, and all of them are weak acids.

Concrete is also reactive. Any kind of acid will erode it.

I would cover the spot with moist baking soda, which is alkaline and
will neutralize acids, and let it sit for a day, then wash it
thoroughly with lots of water. It doesn't much matter what you do,
because the damage to your concrete is permanent.

You can leave it alone, cover it up, or patch it. If you decide to
patch it, I recommend you make a "feature" in that spot. (The first
rule of decorating: If you can't hide it, make it stand out.) For
instance, you could:
* Cover it with a fountain.
* Use a grinder to make an artistic pattern.
* Cut a section out to make a small flower bed.
* Use concrete stain to decorate.
* Inset decorative blocks or stones.

Let us know what you decide to do.

--
Steve Bell
New Life Home Improvement
Arlington, TX