Rapid sps bleaching

[zygote2k]

I've had a Green Acro and a Pink Birdsnest suddenly go from bright vivid color to brown, then to bleach. Also had a hammer coral completely deflate in the same time frame. It happened over the course of the last week.

 

The only noticeable water parameter that has changed was an event with salinity. A new 'fuge was added and the auto top off overcompensated with 10 gallons of RO, dropping the salinity from 1.027 to 1.021.

 

There has always been 5-10 ppm of nitrate on a Hach and Salifert test kit. The alkalinity is very hard to accurately read. Between the Hach and the LaMotte, it ranges from 2.8 to 4.4 meq/l. With the exception of the salinity, the water chem. has been pretty stable.

It is also coming close to changing the halides- they're currently 6 months old.

There is no nuisance algae of any kind in this system.

What things should I be looking for and what things can I try to prevent this from happening?

[Jon Lazar]

IME, bleaching is most common due to large changes in light or temperature. Alkalinity changes may also cause changes in coloration. Parasites like red bugs or AEFW are also a common cause of browning or bleaching in acroporas or milliporas, but not so much with birdsnest.

 

I would suspect the salinitiy change caused your problem. 1.021 is 28ppt, and is a fair bit lower than NSW's 35ppt.

 

I doubt that 5-10 ppm nitrate is causing the problem with your corals, and certainly not the frogspawn. My tank has been hovering around 10-20 ppm nitrate for a couple months with no loss of coloration.

 

Jon

[davelin315]

Did they bleach or did they RTN? Often people will call it bleaching when it's actually RTN, or vice versa. Bleaching is when the polyps remain but the zooxanthellae are expelled. RTN is when the tissue simply peels off. In your case, it does sound like your corals are bleaching as the color went from one to brown to white. There can be a number of different factors involved, but most often it has something to do with lighting - whether it be insufficient lighting or lighting that suddenly shifts in intensity due to water clarity. That's not to say that it can't have something to do with water chemistry or temperature, but it's one of the more common ones (although increased temperature and change in pH can also be common culprits as stated above).

[Origami]

I suspect that this tank may have high DOCs (dissolved organic carbon) and that you're seeing tissue death (necrosis) and not bleaching.

 

The color change from "vivid" to "brown" suggests high nutrients - in this case, organics - rising to sufficient levels to begin to upset the balance of things. I recently had the same thing begin to happen when my skimmer's venturi began to clog with a build up of calcium carbonate. This reduced the air intake which, in turn, reduced how much in the way of organics that I was pulling out. I began to notice that I wasn't pulling as much skimmate out but just didn't make the connection right away. It wasn't until I'd lost a couple of heads of a hammer (that gave me fair warning, in retrospect, with several days of being retracted) that I understood. Another SPS did the same thing you're describing as well - it went from very colorful, to brown, to white in one area before I got the problem under control. After cleaning the skimmer venturi, things seem to have stabilized.

[zygote2k]

Todays' water test with Hach:

alk- 4.0 meq/l

ca- 416 ppm

no3- 7ppm

sal- 1.022

ph-8.16

 

Salinity is still low- can raise it back up to 1.026ish. Pink Birdsnest had complete tissue necrosis, Hammer coral had complete necrosis, and green acro changed from vivid to brown with a few white tips. There is another green acro a few inches away that is unaffected. The Millie and the Monti are doing great. The T. Derasa and the other LPS are also fine.

What else?

[lanman]

Well, it looks like your nitrates are under control. While I had corals turn brown and the tips lose tissue up around 50 ppm Nitrates - I didn't have any STN. Not that I haven't had STN; lost a (fortunately very dull looking) acro frag to it just this week. No apparent reason. Had been fine in the tank for months.

 

I guess I would have to suspect the salinity - some corals just don't like rapid changes - even for the better!

 

bob