nu2reefs- thanks for the kind words and well-wishes. as I've said a few times, I know it must take quite a while to read through it all and I appreciate anyone who has that kind of patience.
Travis- thank you too for the kind words. My main intent on running the thread was to get more information than was already out there. I have learned a TON from all of the people who have contributed their knowledge and the benefit of experience thrughout this thread.
I am happy with the airlifts, although, I have gone back and basically doubled the number of outlets on the blower manifold and placed several more airlifts in each tank to get the kind of circulation I am loking for. All of my tanks have a minimum of nine lifts right now. I do have one sps tank at the moment that has Montipora capricornis. Aside from a few of them losing a little color (so far, just about everything has lost some color), seem to be doing fair. Broken edges of frags have healed and I can see growth upon the healed edges.
The pipe size can't be too big, or the rising air won't pull the water up efficiently.... unless the amount of air can be increased, maybe by inserting multiple airlines into a single lift tube. Other than that, it is more about the number of lifts and using enough to create chaos inside the tank. Just basic experimentation, trial and error, then another trial. One inch pipe would probably work if there were about fifty airlifts in a tank.
One thing I would probably do differently would be to run the manifold from the blower overhead, instead of running down the sides of the greenhouse. That way, I wouldn't have to worry about fixing the airlifts into place. The airlines could run down from the manifold and with the right size hole drilled, the airlift would basically hang from the manifold by the airline.
As far as the height, they should start as low as possible in the tank and the 90 degree elbow on top should be roughly centered at the water level. It doesn't hurt anything to have some up a little higher and some down a little lower. Differing heights makes the flow exit the pipes differently and can help to mix up the flow so it is not all uniform. If the lifts are up a little, the water tends to come out and drop down into the tank. If they are down a little lower, the flow tends to shoot out across the surface more. The air flow rate can be as high as the blower (or other air moving device) can provide. The more air that comes up the lift, the more water comes with it. As a starting point, I would say about .3 cfm.
The gravel makes it very easy to level the tanks. Just scoop a little gravel under the stand to raise it, or scoop some out to lower it. All of the tanks still look level to my eye, just looking at the water level inside the tanks. I think the concrete pavers spread the load enough that they won't sink into the gravel....kind of like snow shoes for the tank stands.
I had to dig a long trench out from the greenhouse and install a simple leech (leach?) pipe for drainage. My original plan was to dump to the ground, but after I had to install the RO system, the waste water was just too much for the gravel floor to handle on a daily basis.
The furnace did have some troubles last winter, but the propane costs are relatively similar even when it is running right. It takes some energy to create enough heat to keep a structure like a greenhouse warm in these cold mid-western winters. Costs about $1,000 per month during the winter. Right now, when it is in the 80's and 90's during the day and down into the 50's at night, the furnace doesn't run at all. The costs also depend on how many sunny days there are during the winter.
chetm2- thanks for the compliments. The thread is made amazing by the number of people who have shared their knowledge. Things are going fair. I am continuing to do some experiments in an effort to maximize the growth rates.
phil5613- Thanks for the compliment.