I have read this thread with great interest, but to me -except for Lances last post - there are three groups that have their predetermined opinion and that try to knock down the opponents using whatever arguments that are available.
Rick and Lance firmly belive in low K, Mike (Stone) cannot accept the good results of Rick because orchids grow perfectly well with normal K-Levels, and then you have David and Catt Mandu that seems more hooked up on the formal deficiencies, as if we were writing scientific papers here.
Ok what has been the outcome of the discussion? In my opinion, anecdotal evidence (and that is good enough for me) has shown that orchids can be grown with low K, but it may not be necessary. There are strong evidence that they suffice with some 100ppm TDS in their water as well.
Orchid roots absorb cations in their velamen (might be so for paphs as well) so nutrition is highly dependent on the balance of nutrients and not so much on the concentration. Actually they do fine with very dilute fertilisers. If the balance is wrong, over time, malnutrition hits in ; much like people getting unhealthy from obsessive sugar intake (thik Rick used that one some time(years) ago). So, continous fertilising with very diluted fertiliser is one clue here.
Possibly, reduced potassium is a good thing as well. Many people use urea or ammonium based fertilisers and the kationic nature of these (NH4+) perfectly fits into the "active sites theory" of the velamen. Nitrate does not btw.
One thing that everyone except Xavier seems to ignore are the micronutrients.
Xavier (Roth) has repeatedly written that the Fe:Mn:Zn balance normally is more or less opposite to the chemistry of wild-grown leaves. You may find more on that in Xaviers thread on "Mineral Nutrition".
The reason why I mention this is that I noticed a growth spurt on my randsii seedlings once I sprayed with Dithane which is basically a manganese-zinc compound. Suddenly they started growing at the speed of normal paphs!
Might be a coincidence? Well that triggered me to look a bit further into this. Some of you may have noticed that many of my plants grow rather quickly. In hindsight, one of the variables in my growing has been that I have been using a rather special foliar feed as part of my fertiliser regime. This had been mixed 50:50 with K-lite. I did that because of yellowing with K-lite alone and so I thought that I needed Urea (which was 50% of the foliar feed). Checking up things revealed that the urea was not the only difference, the balance in the micros was also totally different. K-lite has Fe:Mn:Zn of 0.115%:0.077%:0.077% (approx 3:2:2)
while this foliar feed had Fe:Mn:Zn of 0.02%:0.26%:0.14% (approx 1:13:7)
Not only the balance, but also the levels were quite different.
And more in line with Xaviers findings on tissue analyses.
The 50:50mix produces a fe:Mn:Zn of 0.0675%:0.1685:0.1085% or roughly 2:5:3 balance.
Note that I have used less Fe and more Mn and significantly more Zn than I would with K-lite alone at a given TDS.
Sorry for the long post, though it was about time to share