Mature mixed reef no longer grows soft corals

[peterharte]

My 1400l mixed reef was doing great for the last 3 years, but now my soft corals (GSP, zoas, blastos, acans, and even xenia are stalled or dying, having previously grown like weeds). I have a very large red plating montipora which is growing fine, along with blue stylo, digitata, chalices, millepora. My euphyllia are alive but stalled. Using Triton with chaeto, plus a 10% weekly continuous auto change, plus kalk stirrer. Nutrients fairly balanced between fish and coral, but I run a skimmer and GFO too. Alk consumption is as high as its ever been, so the SPS is thriving. I had some instability a few months back in both salinity and kH, but now resolved, and my parameters are stable for the last two months (440Ca, 1350Mg, 8dkH, 35ppt, 20ppm Nitrate, 0.1 phosphate). No change in lighting or flow or feeding or temperature when softies were flying (although zoas and blastos were always a bit stop start in the tank). Fish are all happy. Water RO/DI is 0TDS. ICP test not showing anything out of the ordinary. All measurements from at least two sources, all probes calibrated correctly. I do have a 50mm/2" deep sandbed which I can't easily siphon clean as the corals have grown out. I also had an aptasia outbreak, and now what looks like green cyano on the sand. Could either of these upset the softies that much? Could the big red plating montipora be outcompeting all else? Or do I have old tank syndrome and if so, how would I fix it? I'm out of ideas, any suggestions very welcome!

 

[Subsea]

ICP test inorganic nutrients. I assume you are carbon dosing, if so, consider your DOC and get Triton N-DOC test at $50.

Also, consider using cryptic sponges in an unlite sump.

 

[Subsea]

ICP test inorganic nutrients. I assume you are carbon dosing, if so, consider your DOC and get Triton N-DOC test at $50.

Also, consider using cryptic sponges in an unlite sump.

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[peterharte]

So I did the N-Doc, but it didn't show anything out of the ordinary. I have found a solution. I eventually decided to treat the green cyano. I had ignored it, thinking it was a symptom of some other root cause. But when I treated it (with Cyano-Rx), all my corals sprang back to life. So either the cyano was causing toxicity in the tank, or another bacteria imbalance was cured by the antibiotics in Cyano-Rx.

I've done a bit of searching, and I haven't seen anyone else refer to this fix to a this problem. I'd be interested to hear from anyone with a similar experience. Hopefully this helps someone!

 

[Shirak]

Acans and Blasto are lps not soft coral. Sounds like it’s mostly things lower down? So despite your no change in flow and lighting there has absolutely been change as the Sps and corals higher up have grown. My guess is light levels have decreased significantly where you’re having trouble now. Have you checked with a par meter? It might not hurt to add another power head lower down too.

 

[peterharte]

Thanks for the suggestions. I have actually solved the issue, and it was a bit unexpected, I can't see any references on this forum for having had the same issue. One noticeable change in the tank was that I got a dusting of green cyano across the sandbed. Not a thick layer like purple cyano, more of a stain. I thought it was just a symptom of wider problems. But in the end, I decided to treat it with Cyano-Rx anyway. The very next day, all soft and LPS corals showed an instant improvement. My xenia rock has even found a fragment that survived. And over the following week, alk consumption has risen steadily, and I've white tips again on monit/digi/stylo. Unfortunately my aptasia has also sprung back into life, it had retracted completely for 3-4 months. So either (a) the green cyano was toxic for the LPS/softies or (b) there was another bacterial imbalance that the antibiotic in Cyano-Rx killed off and reset. And for the first time in my life, I have white sandbed to boot. I see lots of people reluctant to use Chemiclean or Cyano-Rx, but I have to say that it has on the two occasions I used it, cleared my purple cyano with no side effect, and stays clear for usually 12 months. And now it has saved the tank from a complete fail resulting from green cyano.

 

[Shirak]

Hi Peter Glad things are improved! Possible there was something bacterial going on. Cyano is a symptom of something not quite right. Could be you just need more sand sifting critters to keep things stirred up and the sand bed healthy.

 

[peterharte]

So I had definitely got behind on vacuuming the sand. My previous tank was a bare bottom, so this was my first sandbed, and I made the noob error of not washing all the fines from it first. That made vaccing it difficult. I eventually sourced a huge 5 micron 1m long sock, and I was able to vac better then. Secondly, to your point about lighting, we did have a power cut, and I had to reset my Radion Gen5 XR30s after that. I had them set to the Coral AB+ both before and after the reset. But I noticed the spectrum looked entirely different after the reset. So as you say, maybe the lights had drifted or had some software issue, and I was running on a weird mix of colour for 6 months earlier, that may have been the start of green cyano issues!