Carl,
I don't have an explanation other than what I suspect. More or less, I may make rearrangments often enough to change species distribution patterns and thus change water flow, sand areas, light, etc. In my puffer tank, I get Valonia because I cannot put any grazers in the tank besides fish who don't eat it becuase the puffer will crunch any snails or crabs or urchins (but she doesn't touch corals), so I have to manually remove rocks to do it. I think it is close to the same observation you make, and Ron Shimek suggested about a year ago that live rock may become to "stagnant" with coralline coverage to have the same porosity, effeectively sealing the rock to all the different beneficial organisms. I decalcfied a bunch of rock for him to sort through the critters (old, new, and in-between) and although I don't think he's gotten to it, I didn't see any obvious differences...but then again, my rock may not be the rock to use. Maybe we need rock from someone with old tank syndrome. But, it makes sense, even f the pores become packed with detritus instead of coralline. Alternately, it may be the disturbance or "new rock" that winds up shifting the propensity of competitve dominance over time.
My routine is feed ( my food mix above, cyclop-eeze, and DT's oyster eggs, at present) several times a day, and I only add either kalkwasswer (in the small tanks) or calcium chloride and sodium carbonate/bicarbonate to the big tank and the culture tanks - the big tank takes several cups full of dry pellets a day and about 1 cup of carbonate a day! No way to keep up with that using kalkwasser. I do water changes in puffer's tank, but don't do them in the big tank, although sometimes I draw water from the tank for various reasons, and then replace it but we're talking about a very insignificant amount of water in the scheme of the tank. I do use carbon heavily, and have started using ozone - which although I was thrilled with for awhile, am perhaps slightly less thrilled with now as over the past year I am starting to see some declines in sand bed populations and with filter feeding inverts - going to try and circumvent that by feeding even more. I have a calcium reactor on the big tank, but it is (like all my past experiences with calcium reactors) a disappointment and basically a "supplement" to the calcium demand of the tank and just kind of a pain.
The products I use are a commercial soucrce of really great carbon I found that comes in 90 lb bags, calcium chloride in 55 lb bags (usually the 97% pellets, sometimes the 77-80% flakes, depending on prices at order time), and 55 pound bags of a high grade of washing soda (I use Arm and Hammer from the grocery store when I run out in a pinch) and my kalkwasser in Mrs. Wage's pickling lime. Other that the oyster eggs and the cyclop-eeze, I don't add anything to my tanks made by the aquarium industry.
