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comments on Onyx sand
I've had some Onyx sand sitting around since last summer, and finally got
around to using it. I put it into a couple 10 gallon tanks that I have used
for several years now to experiment with different substrates. It's been in
place for 6 weeks or so now, so I thought I would let people know how it's
In a word, It's great.
I like the color, which is a medium-dark bluish grey (darker then it appears
in the bag) and offsets the color of the plants very well. I like the grain
size, which is equivalent to coarse sand and small enough for even small,
fine-rooted plants. I like the weight, which is heavy enough to hold plants
and light enough to make planting easy.
The Onyx was originally dusty, but it washed clean pretty easily. I had a
little cloudiness from the Onyx in both tanks. One of the tanks is filtered
and that tank cleared up completely over night. The other tank is unfiltered
and that required two days to completely clear up.
The plants seem to like it too. It took about two weeks for the substrate to
settle in -- a pretty normal period I think -- and in that time I saw some
nutrient deficiencies appear in root-feeding plants. Since then the growth
has been plentiful and robust. Plants that before I added the Onyx were
growing very slowly or not at all are putting on new growth. Perhaps most
impressive to me is the great root growth many of the plants are exhibiting.
I put identical newly purchased plants in the Onyx-substrate tanks and in a
similarly lighted and maintained tank with an aged sand and gravel substrate.
The plants in the Onyx substrate adapted faster and grew better then the
plants in the sand and gravel substrate.
I have not checked on the alkalinity or GH, which I understand can be
increased by Onyx. My tap water is very well-buffered and I doubt that
increasing alkalinity would have any effect. The water is also very soft and
increasing GH can only help my plant growth. The fish in the Onyx-substrate
tanks are mostly fancy guppies and I doubt they would be effect by increases
in either GH or KH. The color of the Onyx provides a nice background for the