We are installers for the AS system. We generally use a mixture of "Canadian
Blue" gravel. This is a granite gravel that ranges in size from 3/4" up to 2".
Our experience with other gravels has led to using this size as a standard. The
mixture will help "lock" everything together. Many people complain that each
spring the pond awakens to an avalanche of gravel that has all accumulated at
the bottom. We plant all of our plants directly in the gravel. We have never
had a problem using this system in 7 years of business. As for the "muck"... If
you have a well balanced system with added beneficial bacteria, true biological
and mechanical filtration and the right amounts of fish and plants- the muck
will not be an issue. We drain and clean most of our ponds each spring. The
gravel ponds have very little muck in them. We simply pump them dry, rinse or
pressure wash, then pump out again and refill. The bare liner ponds we service
are full of muck every spring! The gravel will act as a bed for the bacteria to
colonize on therefore consuming most of the "muck". We have used smaller 1/4"
to 1/2" gravel in past with no luck. It seems that the larger mix of sizes
allows for more oxygen to get into the cracks and help the bacteria work. The
smaller gravel acted as saran wrap and therefore provided ideal situations for
anaerobic bacteria (not good). Keep in mind that these facts are only from OUR
EXPERIENCE, not from book methods or scientific studies. My advice is to value
everyone's opinions in here as they will all have valid points to learn from. I
hope it helps. Also, remember that the gravel pond is for the POND hobbyist.
Many KOI hobbyists may argue the gravel "can of worms." Read into it and use
your best judgement.

PS... That "prof installer" that made a 4 foot pond and filled it with 2 feet
of gravel should not be called a professional. The AS system requires a very
thin layer of gravel and would never instruct them to add 2 feet of it. They
should not be called a professional for that job.

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