I don't know how accurate the info is, but I have been told (by the sole hydroponics store in Wilmington NC) that the original Hydroton is no longer manufactured. It may be that someone bought the name and is using it on a different manufacturer's product. The shop now carries CYCO Hydro Clay, which I find to be acceptable.
The only one I avoided like the plague was Aliflor, and that was because they used kerosene or diesel as the binder when making the pellets, anticipating it would burn off during firing, leaving extra porosity. Unfortunately, several container hit the US that were underfired, so reeked of fuel and killed anything planted in it.
The color of the clay is, to some degree, controlled by the raw materials, but might be a remnant of the firing schedule, as well. Terra cotta clays contain a lot of iron. If fully oxidized, they are beige to peachy to orange color. When the firing atmosphere is fuel-rich and a reducing environment, they will be gray. What often happens is the firing is a bit fuel-rich to drive off the additives used to form the pellets without oxidizing them, but when air hits the still-hot product after firing, the surface starts oxidizing.
There are a number of properties that may make one brand better for an individual than another:
►Particle shape - spheres offer the most fee void space, but easily move around in the pot, acting like a container of marbles, making it harder for the plant to stabilize itself.
►Particle size distribution - the narrower, the better.
►Average particle size - the larger the particle, the larger the pore size between them.
►Surface texture - smooth = better wicking.
►Degree of absorption of solutions - more = better wicking and duration between waterings.
►How much of the absorbed solutions are readily released again - more = slower mineral and waste buildup.
►Chemistry - I have left this for last, not because it's unimportant, but because I've learned something recently:
The LECA I have used over the past several decades have all been pretty much chemically neutral. I even left some sealed in a container of distilled water for a year, yet saw no rise or fall in pH. However, Miss Orchid Girl has moved away from S/H culture because the only locally-available LECA for her was formulated with an alkaline clay, so the rhizosphere pH climbed over time. COnsidering the low water solubility of these material, I'm not sure how you'd test that before use.
