I think ray has it spot on. If one has to prove that penac is actually of some benefit then you have to use a control tank which has everything exactly the same (or as close as possible) as the original tank with the exception of Penac. Without a control to compare against, any inferences from the behaviour of a single penac enriched tank is quite meaningless. Whether you like Tom Barr or not, he does carry out all his experiments using control tanks. Of course he could still have done them wrong, or if you don't wish to believe him, that is fine too, but you need to carry out the experiment for yourself, with a control tank and then prove to yourself (and everyone else) that the Penac was actually beneficial.Well I'm a scientist and I have to admit that the world is a lot more complicated than anything science can predict.
There is a lot of interest recently in the power of prayer in medicine. The classic study was done in 1999. Here is a reference:
If prayer can improve the outcome of cardiac patients, I'm not surprised that penac can help plants.
OK here is a suggestion. Set up two identical aquariums. In the first, control all the inputs as carefully as you can but don't use penac. In the second, do the exact same thing but use penac. Report your results periodically. If there is a difference, note what it is. This way everyone can repeat what you did and decide for themselves if penac works.
Art, you mention that your tanks seem to have done very well with Penac. However we all agree that planted tanks are extremely complex and plant health and growth is dependent on a vast variety of factors. Without having your control tank it is a little meaningless to ascribe the perceived better plant health to the single new variable of Penac since it could very well be down to a combination of other factors and have nothing to do with the Penac.
If we can't perform this experiment (lack of money and time are of course valid reasons) then an attempt at understanding it's effect can only be made if ADA were open about Penac and we could actually know exactly what it is. At least then we could try to deduce what possible advantages it could potentially have for planted tanks. But without that knowledge, the only proof can be from a controlled experiment as suggested by ray. Tom carried the experiment out and it didn't seem to do anything much for him. If others manage to do similar experiments and find that the Penac is actually beneficial then I will believe in the usefulness of Penac.