Many interrelated factors go into the optimal growing of orchids.

Ray, good questions. I tend to doubt that growstones provide much silicon, as you say even the most soluble forms of SiO2 are pretty insoluble in water except at high temperatures. But I did assume that after an initial soak there would be little or no leaching of anything else from them and that they would not affect pH or TDS appreciably, rather than just testing it, which is easy enough to do.

I'm not really worried, since we've been using them for a while and the early adopters show no signs of toxicity,but there's no reason not to know ... so I'll start a test with some later today.

Steve

Hygromite is a good replacement from diatomite. Most hydro store carry it or can get it.

Ironically, the silicate in glass doesn't become soluble unless it's in a very high pH solution. On the other hand, low pH will not degrade the glass, so the growstones would be safe to use with pH-adjusted water.

Granted, it is a slow process, but standard soda-lime glass, when exposed to water, actually becomes pitted as the water reacts with the alkaline mineral ions, making them soluble, and extracting them into solution.

I have a prohibition era whiskey bottle recovered from Long Island Sound, and it is iridescent, thanks to that extraction.

After the previous round of posts on this topic, I did start some tests on the Growstones. I won't post the whole sets of numbers here, but basically I started with water right from my RO (TDS < 5, and, after sitting exposed to air for a while, equilibrates to about pH 5.7) and just covered some Growstones straight from the sack with it. I covered the beaker tightly to minimize evaporation, and checked TDS and pH at roughly 24 hours intervals. Over the next week or so, the TDS went from 1.3 to 133, while the pH went from 5.7 to 9.85. At that point, I drained the water and replaced with fresh RO water and did another week, at the end of which TDS was 60 and pH 9.7. So I'd say Ray is right to voice a concern, though I don't know how serious a concern it is yet, since it doesn't take much to really swing the pH of unbuffered water. My next set (nothing happened during the holidays) will involve some daily rinses (which we already do with bark and CHC), and also see what happens in buffered water, such as the fertilizer solution we use. But it definitely got my attention, and I appreciate Ray pointing out the possibility.

Steve