RTN questions

[Exterminaans]

OK, sorry if these questions have been answered in another thread, but I haven't found anything that specifically addresses them so far. I have a number (3)of acropora frags that have died, 2 of which I suspect could be RTN, and a fourth that is not looking so good, and I would like a little better idea of how RTN plays out, in order to rule that out as a cause. Is there any warning at all from the appearance of the coral prior to the tissue "peeling" that the check is in the mail, so to speak? How rapid is rapid, usually? Is it similar to say, ick, where once it occurs it is present in the tank until you leave it fallow of corals for a certain length of time?

Those are some of the questions I have, and now I will go into specifics of my situation. I had a blue turaki frag that seemed to be doing fine, was in my tank 1-2, maybe 3 months, but then started turning brownish over the course of several weeks and then BAM, tissue just started peeling off of it and was gone in a few days. I had a Acropora loisette frag that was in my tank less than a month. It was bright green and started losing color soon after I put it in, and probably over about 2-3 weeks turned brown and stopped extending polyps, the tissue was still on it last night, but tonight about half of it was gone, so I just pitched it (this was only about a two inch frag. I have another Acropora papillare that is looking a bit "thin" and has some algae growth on it. I upped the flow on it a few days ago and am getting more polyp extension now, so we'll see; and low flow could very well be the cause if it's decline, just not sure.

My parameters are:
29 GAL Biocube
SG: 1.025
Nitrate: 0 and has been for several months, no nitrites or ammonia either.
Phosphate: 0
Ca: 465
Mg: 1410
Alk: 9.3
Temp: 76
Lighting is 150watt metal halide with 2 18 watt T5s (Phoenix 14k for the MH bulb).
Another factor could be the water I was using. I just found out it has a TDS rating of around 30ish and so I switched to another source that I have been monitoring the TDS on (RO/DI water from my LFS), but that has been only for the past 3 weeks, I think.
I also had a high-ish alkalinity issue (11 dKh) that I have resolved. I thought my pH was way out of wack at that time too, but have narrowed it down now to miscalibrated probe. I re-calibrated it and it appears to be normal now. that was about 2-3 weeks ago that it was resolved and it lasted about 2-3 weeks before that too.

All thoughts are appreciated and I will provide any information I may have missed, if asked.

 

[Mike Johnson]

I wish I had an answer to this. I've had more than one coral RTN. Once had a soccer ball size, 3 year old birdnest, RTN in a day? Here's a good link:

http://www.reefs.org/library/aquarium_net/0498/0498_2.html

 

[yvr]

I agree with Mike, RTN can happen really suddenly on a seemingly healthy coral that has been in a tank for years. I've lost a few corals the same way too. I keep an eye out for any signs of RTN and immediately cut off the receding/ dead parts and dip the entire coral in an iodine bath like TM Pro Coral Cure. I prefer to be proactive when I see tissue recession now.

 

[Choff]

I had a bout of RTN and everything I read in my case pointed to my high Alk. I had been sitting in the 10-11 range for weeks.

 

[Exterminaans]

Hmm, well that information is interesting Mike. Thank you all for the input. All the corals I have lost have been Acroporas, which I is a new "level" of more sensitive coral that I have just started trying to keep, along with some montiporas (which are all doing fine). I think this is mostly a matter of struggling to figure out the needs of the acros, (mostly water flow) along with a few errors that led to a parameter getting out of whack at key times. All the lost corals started with days or weeks of poor polyp extension, either from the moment they were introduced into the tank or shortly after, as well as some color loss, followed by a last few days of tissue recession/sloughing. I always struggle when a coral is unhappy (which of course is harder to judge if you have never kept them before, and are unsure exactly how much polyp extension to expect), as far as when to move them, and when to leave them alone.