Question
QUESTION: My daughter installed a small backyard pond & waterfall in Houston with no fish or plants.  The stones have turned brown on the upper surface only.  It receives little sunlight.  The scum is gritty, not slimy.  Could this be a pH problem or Ca build-up?  Chlorine does not help but Lime-Away seems to dissolve coating on pebble.  What do you suggest?

ANSWER: Hi Susan,

Does the water come from a well?

The  water is probably too rich in minerals, or, what we call "hard water"

Please let me know.

Carlo


---------- FOLLOW-UP ----------

QUESTION: Thanks Carlo, it is not well water.  It is city water run through a water softener.  Could it possibly be the rocks which make up the pond edges and waterfall?  They are large flat reddish rocks.

Answer
Hi Susan,

Do you know where those rocks come from?
It looks like they have a high iron content.

If that is the case, the only solution that I know of, would be sealing them with clear marine varnish, or a more expensive epoxy resin.
Please check the link below for more information on iron in water.

Keep in touch,

Carlo

http://www.water-research.net/iron.htm