Trying to get a handle on my RTN/STN

[LebaneseDlight]

Over the last month, I have lost 3 SPS frags, and a 4th is in recovery:

 

- Strawberry Shortcake, was never doing great from the start, went from meh to completely white overnight

- Pearlberry frag was seemingly doing well, great polyp extension and decent growth, and then RTN'd at the tips; tried to save it by fragging, but to no avail

- Bird of Paradise Birdsnest, overall was great, but had a small white spot on the base (not in a shaded area). I tried to frag that part out (didn't realize it was hard as a rock) but didn't have the proper tools

- My red Planet is showing zero PE on the base, though the branch still looks good. Doesn't look bleached or RTN, just no PE on base, so you can see the little holes where the polyps are retracted. A week prior to that, looked like white stringy coral poo coming out of the polyps on the base (I blasted it off)

 

Whereas these frags obviously were bad news, my other SPS frags (branching, tabling Acros, monti digis, birdsnest, etc) are showing good growth and PE.

 

Here are the events that led to the RTN/STN:

- I was not monitoring temp. I know. After the first events, I brought out my digital thermometer, and the temp was going from 76 at night to 86-87 at midday.

- My Phosphate level was at .30, and I got a phosban reactor and quickly brought it down to 0

- My Mg was elevated at 1700-1850 for about 2 months

- I bought a Tunze 9002 and reduced nutrient levels across the board

 

Otherwise, Alk was constant/stable at ~9, Ca at 450 (through 500, depending on Mg levels), Sg at 1.025-1.026.

 

I do not dose often at all (other than dosing Kent Tech M for those two months), if anything, just the Alk part of the 2-part. I do weekly 20% WC with Tropic Marin Pro which keeps my Alk/Ca at those high levels.

 

I have my Chiller up and running, so temp is a constant 78-80 now. Mg is at 1500, so not ridiculously high anymore. Daily top offs keeps my salinity stable. All in all, everything is looking pretty OK for now (though my Red Planet is still not showing PE at the base) - but it's only been a since the weekend with the chiller, so I'm not counting my chickens before they hatch...

 

Although no one can tell for certain, what went wrong, I did not lose any SPS before this month and I've been transitioning to SPS dominant tank since last November. All my RTN/STN events took place within a week - a hot week in my condo.

 

Do you think it's safe to assume that these events were triggered by: constant high temps and big temp swings over a period of weeks, coupled with a huge drop in phosphates in a short period of time, and perhaps the added stress of elevated Mag levels?

 

To add, I do have a number of LPS, and am beginning to get worried that chemical warefare may be an increasing threat, and given the expense of these high end SPS frags and mini colonies I have, I'm thinking it's time to set up a second tank for my LPS or sell them...

 

Thanks, oh wise SPS gurus, for taking the time out to read this long thread.

[lakshwadeep]

What are your test kit brand(s)?

 

Temperature swings can cause RTN; that happened to me when I had a nonfunctioning heater. Another problem is RTN can spread.

 

What type of other corals are in the tank; and what are their relative distances to the sps frags?

 

A good general approach to stopping any necrosis is to have extremely stable water parameters, which is what you're doing. An ATO is a possible addition for stability.