Tony, bugs treated with Interceptor, the heart worm med from the thread on RC and RDO.
My Ro is fine, TDS reads zero. I changed my reactor media completely before any of this happened. Maybe bad media? Don't think so....

Brad Wrote "I also know it wasn't coming out in any appreciable amount."

I am curious how you knew that phosphate was not exiting in an appreciable amount? Any interesting test I don't know about.

No, nothing cutting edge. Since I use no macro algae, and kalk only sparingly, this makes me confident that PO4 input is greater than export. The import is confirmed by fairly heavy feeding on my part.

Interesting. I've never thought about PO4 and how it might be affecting my system. I guess it wouldn't hurt to try a sponge. What's doxycycline?

Mason, doxycycline is an antibiotic prescribed for vibrio infections. Julian Sprung first announced it for treating elegance corals, and I researched it a lot before dosing. It isn't something I would recommend as a first (or second) course of action. I found that if I scratched my arm while working in my tank, I would get a large blistered infection at the site of skin breakage. This led me to believe that I might have an excess of vibrio bacteria in my tank. With the chain of events (DSB removal, high temps, excess SPS mucous), this was feasible for me. After treating, I did still experience some tissue loss. I have also worked at keeping my temp below 80, as this inhibits vibrio activity (so I've read).
I have also had a outbreak of algae in my (attached) frag tank, leading me to believe nutrients are at least partially to blame. NO3 is not detectable, and never has been. PO4 is the same, but not all PO4 is detectable. I believe this is the nutrient in question. And before anyone asks for proof, all I have is "guessing".
I've become very frustrated with all of this, and it's been going on for some time. I'm open to any suggestions at this point, although it looks like I haven't lost any tissue for about 5 days. And to reiterate, it is only acropora sp. SPS that are having this problem.

Interesting problem...but I don't see how phosphates that aren't being detected are contributing to the RTN problem.
My reasoning...
Whether it is DOP(Dissolved Organic PO4), DIP(inorganic) , POP(particulate organic), PIP (particulate inorganic)... These types of phosphates are linked through a cycle in your aquarium. If you are reading a zero when measuring DIP (most test kits - Salifert incl.) then
it is unlikely that your other phosphate based constituents are out of control.
There is a neat article with a brief display of these cycling PO4 forms:
http://www.reefkeeping.com/issues/2003-04/eb/

This doxycycline business is kinda freaky...I wonder how Julian came to these conclusions? (doxycycline/nitrofuazone and elegance corals) and how they apply to RTN in SPS corals. I would love to see his research but there doesn't seem to be any...I would appreciate a link because I couldn't find anything more than his speculation about the rising mortalities among elegance corals.

Brad, Mason,
What about the growth of your acros and other SPS and their changing water flow requirements as they become larger? I know you have been doing this a long time, but are these colonies getting larger or are you fragging them a lot?

What are your pH fluctuations between day and night? Have you considered turning your reactors off(down?) at night or dripping Kalk only at night to compensate for low nighttime pH?

Hope these thoughts help...

Stephen

It looks like Julian has kept his research "secret", because I couldn't find it. Eric Borneman actually did an article refuting Julian's claims, but some people found that it did slow/stop RTN in acros.
As for size, no, I don't see any correlation to flow. I have always adjusted flow to compensate for growth, and this STN affects frags just as often as colonies in my tank. Also, my birdsnest is getting to be the size of a soccer ball, and does not show any tissue loss.
My pH is fairly constant over 24hrs. never going below 7.9. My reactor discharges into a high flow area right above the skimmer intake, so CO2 doesn't seem to have negative effects. However, I have turned the reactor down anyway, in an effort to reduce alkalinity. I have about 7000GPH of flow in a 150g tank, and the surface agitation keeps the gas exchange movin'!
The only other info I've found to explain this tissue loss is PO4 accumulation. I agree with you about PO4 cycles, but I don't have any better ideas to follow. And I certainly didn't see the harm in adding a PO4 sponge to remove my invisible phosphates! The trouble with my entire procedure is that in a desparate attempt to save my corals, I make multiple changes over a week. If/when this all stops, I won't know which change/combo eliminated the problem.
I gave someone a bunch a frags as insurance, and they are all doing well in his (newer) tank. So what does that indicate? Nothing maybe, but it does seemto be something in my water, whether chemical, biological or physical.

Most likely correct Steve, however some interesting reading on lowering alkalinity and the reversal of RTN, by some very experienced sps keepers. Also, the theory, is backed up by many German sps reefers, according to the threads.

So what are these people considering as a lower, RTN reversing alk setting?

I believe 8 or 9 was suggested. Although you're in that range already, correct?