Onyx Sand vs. Play Sand

Onyx sand contains elements like iron, calcium, potassium, etc that plants use for nutrients. Regular sand doesn't contain anything and isn't a good substrate for plants alone. Is it worth the money? I think so. If you want to save some money, you can mix playsand with onyx sand, with the onyx sand composing of at least 50%.

Onyx Sand, Flourite, and all the other "special" substrates have one thing in common - the all have excellent CEC or cation exchange coefficient/capacity. This means that they can bond minerals impotrant to plants, on the outer and inner surfaces, in a form and manner that makes them readily available to roots. Plants to which substrate feeding is important respond well to the nature and texture of these substrates, actively growing into the particles.

Sand is basically inert and all but totally lacks this function. It also is prone to anoxic areas, bad for plants and fish alike.

Do you really believe that experienced growers pay the premium for special substrates which perform no differently than would sand? I promise you, we are not all either gullible or stupid, although admittedly some are - just as in area.

To a certain extent you can add it to the water column, but sand does not have the poroisty and the reductive areas that onyx does.

I've done the water column exclusively for about 10 years with plain sand, you can do it, but it's much easier to use something like onyx sand etc.
Some plants do need it to do really well, vs okay, many don't care though.

Regards,
Tom Barr

I use onyx sand in my tank. I like the look, it ends up a dark charcoal grey. I agree the others about the benefits of onyx sand, but it does cost a ton. I've seen people that say they have good results with small natural gravel and laterite/flourite as an additive, probably cheaper to go that route. Onyx sand will also add a little kH to your water, also. (not much.. with my water, the GH and kH out of the tap is nil, and the sand raised it to about 2 deg. kH) I added a small handfull of tiny seashells to the filter box to add a little bit more kH, and it stays about 4-5 now. IMO, unless you have very hard water or high kH water I wouldn't worry about the added kH.

Also: Some plants don't get minerals from the water column anyway, or at least not as well as some others. (the reverse is true, also... some plants don't seem to give a hoot about minerals in the substrate, they adsorb what they need/can from the water)

Aquatic plants do the same even if you remove the roots if the water column is supplied.

But a few species might better with both, still, one could certainly argue plants prefer leaf uptake, not root uptake based on the available research.

Not every plant has been tested though(maybe 30 out of the 300 or so).

Regards,
Tom Barr