Today was the day. Got some questions:
Q1) Is there a special wrench or trick to remove the adapter base (Fleck 2510) from the tank? The pro who installed this didn't intend for it to leak or ever come off the tank. After beating it to break the seal, I used an oil filter strap wrench to turn it off; it didn't give up without a fight. There was evidence of a setting thread sealant on the threads I'll have to chase off somehow.
Q2) What should you use as a thread sealant/lubricant? Local softener guy said any Teflon thread compound. I used RectorSeal® T Plus 2® pipe thread sealant, a non-setting, multi-purpose compound.
Q3) Is there a standard kit of O-rings to replace the external ones, or do you have to order them individually? My tank O-ring was flat on the tank side, so I inverted it for now; old trick, sometimes works. What about O-ring lube? I used Dow Corning #4, because I've used it on lots of O-rings in other applications.
If either of these sounds really wrong to anyone, I'd like to know so I can clean this job up, and do the softener right in a few weeks.
I had prepared the new tank last week by washing it with a weak bleach solution, setting the distributor tube and basket, dumping in 1/8-1/4 stone (also sterilized) to cover the bottom basket, and finally filling with Centaur carbon (1.5 cu ft of the stuff, according to the box). I then filled the tank with conditioned water and let it sit for 3 days. Today I ran water through the distributor tube for 10 minutes at 1-2 gpm to flush out the fines, and finally moved the valve to the new tank. I'm only left with about 10" freeboard + top dome in a 10x54 tank, so I added an upper basket to the valve. Ran 1 backwash cycle, which on my valve is 10-min backwash @ 5gpm, 8-min pause, plus another 4-min backwash @ 5gpm. I ran this cycle into a bucket so I could see the progress as the water cleared up, and measure the flow.
Now to the old tank, which will become the new softener tank in 3 weeks. It was only 50% full -- I don't know if the carbon leaked out and I'll find evidence of that in the softener tank, or I got ripped off when the pros rebedded it 9 1/2 years ago, or they were just wanting 50% freeboard. The distributor tube & bottom basket came out easily and seemed OK. The carbon looked fine -- it was loose, not obviously contaminated with anything. Getting it out was pretty simple once I gave up on trying to pour it out, and fell back on using the ShopVac. Somebody at the Bureau of Standards really screwed up, because the standard 2 1/2" ShopVac extension and hose fit nicely into the 2 1/2" opening in the tank. I sucked out all the media and gravel and dumped in into an old brine barrel with a leaky bottom. In a few weeks I'll lay it out to dry on a sheet of plastic, and recover the gravel.
One last comment. I had always felt that the chlorinator wasn't really doing a proper job of getting the iron out (1.3ppm Fe). I had been using a basic swimming-pool chlorine test kit and trying for 1-2ppm "chlorine", without really knowing what I was measuring, on the advice of the pros that installed the system many years ago. Last week I flushed the contact tank (yuck!), pressure-washed it, and refilled it with the chlorine pump set up a little higher than normal. Today I broke out my shiny new Hach Free and Total Chlorine test kit, and found Total Chlorine of 2.5, Free Chlorine of 1.9, and swimming-pool chlorine off the scale (above 3.5) coming out of the contact tank. I'm not entirely sure what all this means, but I suspect my historic chlorine dose was inadequate, and it might be a little high now. Advice welcome.