EC,
While I can respect your viewpoints and would like to learn more about your experiences of the past, it seems you have made up your mind based on your past experiences and seem pretty closed off to any potential differences between what you did and what many are currently doing. I, however, made the mistake of assuming the experiences you have had based on what I have encountered from others making similar statements.
I can appreciate your wanting to get answers to the posed questions, because it means that you're trying to find out if there is something that has been learned that you didn't already know, and you're asking me to prove it. Well here's what I will admit - I've read many studies in whatever spare time I've had, but with owning a consulting business and having 4 kids at home, I don't have a lot of spare time to really dig deep into this information and I don't have anything bookmarked to whip out and post. So your statements that I should know what I'm talking about before making various statements is only partially applicable in my opinion. I can't reference the information offhand but it doesn't mean that I didn't read it and decide if it was pertinent or not enough to consider or discard when I was learning about scrubbers. Much of the information I read was mind-dulling scientific papers that I read years ago, so I didn't "study" it enough to be able to recall it and give you an explanation which you appear to desire. Sorry I just don't have the time - if I didn't have a full time job and a full time family, I would probably have all the answers - I am the type of person who does want to know this information because I get into this kind of stuff and obsess over it. Unfortunately I don't have the free time to obsess anymore without making my wife very upset LOL.
I have had similar discussions in person and what it comes down to is that I have done enough and seen enough to have what I consider to be a very good grasp on what works and how to make it work. Admittedly, due to lack of obsession time, I don't have all the information that folks such as yourself really want to hear with regards to the precise mechanism that makes it work and why it works the way it does - my knowledge in that respect is much more of a general understanding, so you are correct that some of the statement I made may have overstepped my bounds of recollection and interpretation of what I have read and found to be pertinent.
I do appreciate the fact that you tried many different approaches of this method in the past. It shows that you are/were open to new concepts. The algae scrubber was a new concept to me that I read about after I joined the online community (which didn't really exist when I got out of the hobby 12 years ago) after I got back into the hobby a few years ago. So while you approach this subject with experience from the past, I have been approaching it from only knowing what I have read about the way most people did it in the past compared to how it is done now.
That certainly puts me at a bit of a handicap when it comes to me assuming that you did the same thing - perhaps my mistake. However, a few things you mention piqued my curiosity and other things were telling of you not being aware of a few differences:
- From most of what I have read, yellowing of the water was caused by people removing the algae from the substrate without removing it (substrate) from the system first. It is also caused by the "roots" of the algae dying from lack of light, flow, or both. In the middle of writing this, you posted about the algae life cycle, and mention algae insuring it's own survival by fractionating to decompose and provide the next 'generation' with nutrients. I put to you that if you provide a situation by where the algae grows fast enough and is harvested frequently enough, part of this life cycle can be cut off. Meaning that if you allow the algae to grow at close to the rate at which nutrients are provided via the water flow, and your lighting/etc is set up properly, you will have less of this "death" occurring, and if the algae is harvested before it gets thick enough to start dying, you have significantly reduced the "death" portion of the life cycle. Perhaps I am missing something, but that would explain why what I am doing now seems to work so much better that what others experienced in the past. I have ran an algae scrubber almost exclusively on one particular system for almost 2 years, and when/if I ever pull water out of the system into a white bucket, it is as clear as freshly mixed saltwater. While I have not compared this to, say, water from a tank running ozone or made a before and after comparison of the water before the scrubber was installed vs after, I can say from general experiences with look and smell of water pulled from a system that the algae scrubber does a very good job of keeping the water clean and clear (excluding particulate matter, just talking about color of the water). So I guess my question is that you experienced yellowing of the water and you were removing the substrate from the system to clean/remove the algae, and you were doing so before there was any death of roots, why am I (and almost everyone else currently running algae scrubbers) not experiencing the same thing? Keep in mind that most people running horizontal or even slanted scrubbers have a much, much higher incidence of problems that are typically attributed to ATSs, and this is specifically related to the fact that single sided screens (horizontal, slanted or even vertical (lit on one side)) have a much higher rate of death at the roots due to lack of light. Vertical double-lit screens can go much longer between cleanings before this happens.
- You bring up references to biology of the organisms, type/strain of algae grown, etc. This goes back to my lack of time to obsess, so my answer can only be less specific than what you desire. From my understanding, most older devices were dump-bucket or surge-style scrubbers. I believe that this is what most people who have just a passing knowledge of the old ATSs think of. Those devices, again, from what I understand, were prone to growing the slower-growing red turf algae mainly, because red turf grows well in those conditions, whereas green hair algae does not fare as well. My experiences with this concur with this assumption, because in certain areas of certain scrubber setups I have maintained, I will get red turf growth and it is difficult to scrape off when compared to GHA.
- W/R to lighting: this has been a field I have been involved with outside of the aquarium world more than in (until I got back into the hobby). Specifically I have attended several lighting seminars that were focused on commercial/architectural/industrial subjects, and while that doesn't directly translate, it has a strong parallel to aquarium & plant growth lighting w/r to technological advances. While I don't doubt that there was available light of good intensity and I don't doubt that you were able to grow large amounts of algae, the lumen/watt output of various light sources has steadily increased over the past few decades. This means more intensity using less lamps, and when proximity of lamps needed to achieve a certain lumen level, you reach a point of diminishing returns with respect to reflectors being too small to maintain efficiency. Smaller and/or more efficient sources such as T5HO allow more efficient use of the light. When it comes to LEDs, there is more than enough data from the plant growth community to show that the levels of light provided by LEDs in the specific spectrum needed in order to grow plants is in a world of it's own, both from a power usage standpoint and from a growth output standpoint. When it comes to algae scrubbers, this again is more of a parallel course than a direct correlation. I can't say with definitive certainty that one particular LED spectrum performs better than another when it comes to algae (because there has been no study that I have found that directly correlates to what we are doing), but based experiences by myself and others, it certainly seems to be that the case with plants is the case with algae - it grows very well under LEDs, and the potential level of intensity is in a class of it's own, due to not having to deal with reflectors to re-direct the light from the back of the lamp around to the front.
- W/R to types of algae. Really what I was referring to is the color and consistency, as I will try to explain in more detail. I am not claiming to have created anything new. I am also not claiming to know exactly what species everyone is growing. It just may be that via the recent surge in use of this method and the speed of information sharing today has allowed more collaboration of this information through trial and error, and it just very well be that this allowed those of us using algae scrubbers to really narrow down exactly what conditions are needed to make the growth as optimal as possible, while minimizing or eliminating the problems of the past. So I do not have documentation to support this, however I do have the collective experiences of countless others whom I and others have assisted in troubleshooting various issues with the algae scrubbers. There is a direct relationship to the amount of algae grown and the amount of food provided to the system. There is also a relationship to how this algae grows, depending on the size of the substrate, and the duration and intensity of the light provided to it, and the flow rate of water provided to it. Keep in mind that this is mainly applicable to the vertical double-lit scrubber. What happens is that if you have too much substrate and too much light when compared to the amount of feeding, the algae tends to turn a yellow or caramel color and it rather gooey to the touch. If you take the exact same setup (system/tank, etc) and more properly match the screen size, lighting duration & intensity, flow rate and feeding, the screen will grow mainly GHA. If you take the same system and provide too much food compared to the capacity of the scrubber, it tends to grow a darker brown algae, and in extreme cases (poorly maintained, high nutrient tanks) it can grow black and oily. The darker algae and yellow algae tend to block light to the substrate, causing the "roots" to detach and release algae (and likely toxins) into the tank (see previous paragraph). The green growth has less propensity to block light, until it grows very thick. So with this taken into consideration, a square inch of algae does not necessarily equal a square inch of algae. On that subject...
- The 3D enclosed box method is something very different and I do not believe it was ever tried in the past. Basically the vertical screen is in a placed in an enclosure that is open on top (for access) with a drain on the bottom. This allows you to place the light very close while keeping it protected, but the primary effect is that if the chamber is narrow enough when the algae growth becomes thick enough it spreads out horizontally, and when it touches the windows, it traps water and allows the growth to become suspended while still allowing water to flow by fast enough to minimize boundary layer effects. The act of suspending the algae in this fashion allows better penetration of light to the base substrate, keeping the roots alive longer.
- DOCs. I can't remember where I read it, but basically if you compare the levels of harmful compounds produced by algae under high-intensity, short duration photoperiods versus lower-intensity, longer duration photoperiods, the latter will tend to grow more brownish or darker and produce overall less efficient results, while the former will tend to grow more green algae, until the photoperiod becomes too long in which case the algae turns yellow/rubbery. Again, this has to do with type of growth and the light-blocking tendencies of that growth, which correlates to roots dying and thus the problems associated with ATSs of the past (generally). Also GHA filters better than the other extremes, for many of the above reasons.
- N and P - written too quickly. What I meant was that N and P are absorbed by just about any algae that you can get to grow.
- What do you mean when you wrote "We grew lush green algae. Getting the algae to grow was never a problem. Learning how to keep it from growing was a much larger challenge."? Keeping it from growing where? In the tank?
Over the past couple of years, I have helped many others work through issues they have had with their scrubbers and systems in general so that they are getting the desired results. I can't tell you how many people have told me how quickly their system conditions improved after implementing a scrubber. There is certainly a distribution of experiences, but the vast majority of them are positive. Very rarely do I come across someone who had a bad experience. Occasionally I come across someone who tried it but just preferred another method over it. In terms of the ratio of positive to negative experiences that I have seen, current users of algae scrubbers on average seem pretty satisfied with the method.
You do make a valid point about long-term issues. But who is to say that some of these issues have been eliminated due to current practices?
And, while I have to agree that you see tons of algae in Dr. Adey's tanks, why is it that I have no such algae growing in my system, and very rarely have had any of any significance? Why is is that countless people using this method today have eradicated algae out of their tanks on a consistent basis? This is why I keep going back to saying that there indeed are major differences in the means and methods of yesterday and today.
So all in all, you state that back in the day, you tried pretty much everything that is being tried today. After reading this, do you still feel this is the case? Can you at least accept the fact that, at least based on the circumstantial evidence, something is being done better now?
Wasn't assuming, just was stating you have a skimmer 
Regardless......It is irrelevant. One square foot of algae growth is one square foot of algae growth. 
