Mr. Saltwater Tank Friday AM Quick Tip #143: Got Coral Death or Stress? Look Here For Answers

Coral death or stress (often known as “bleaching”) is NOT fun. It often starts and stops for no reason and finding the cause often feels like climbing down a rabbit hole of endless turns. When I am looking for the source of coral stress or death, here is one place that provides many clues.

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Comments for this article (27)

  • David Wood says:

    Hi my name is david and I just wanted to ask I have a 300 leater reef tank that I have had sucsesfully for about 3 years naw and am having truble with my scimer so wanted to change to a better one but befor I wanted to buy one I just wanted to ask you what you think the best scimer on the marcet is at the mo as I have a aqua one scimer at the mo ,, but it has to ba an external scimer as I dont have a sump so have to rely on one that fits to the back of my tank

    thanx for your time and help ,,, ps love the videos realy helped me a lot grow my tank to what it is today

  • Klaas says:

    Mark. This wasn’t very useful information to be honest.

  • Klaas…thanks for feedback.

  • Andy says:


    For two years now, I have had ZERO coral growth in my tank, whether it be from SPS or LPS corals. I have a 24x24x24 cube, with a great skimmer, 2 MP40s and 250w Radiums on a magnetic ballast. My parameters have always been perfect and are controlled via a Reefkeeper. I am close to quitting the hobby because for five years I had great success, and with this (new) two year old tank, I have frags that are still frags.

    I do weekly 10 gallon water changes using ESV salt, and hardly ever miss one. I know this is not a ton of information for you, but the online forums are full of people that don’t know anything, and the ones that do seem to give conflicting information. Any ideas?

  • Andy says:

    I should add that the colors are very pale as well.

  • Duane says:

    Sorry Mark, but I agree with Klaas. When I saw the Quick Tip title, I was excited to maybe get a suggestion to help my problem. My 180 reef tank has been going great for 4 years with intense coral growth. In the past couple of weeks I have polyps actually dropping off my Millepora in huge sections within hours. Several other corals look sick as well. Water perimeters are good. I have all the tests kits and use them regularly. Even used a friend’s test kits to verify my test kit results. Have no idea what is going on. Guess I will have to keep doing big water changes and ride it out. Mark, you always have great tips and I have learned a lot from your videos (I look forward to them). I guess, you can’t hit a home run everytime!

  • Joshua says:

    Well I really enjoyed the information Mark thank you.

  • Chris Goddard says:

    Guys just remember people of all levels watch these tips. So just cos it hadnt benefited you doesnt mean it hasnt someone else.

  • Merne says:

    Good tip. Most people don’t think what happened 2 weeks ago, and from the quality of comments on here, I can tell people are only looking at what’s happened in the last day or two. IMO, when someone says things like “I have all the test kits and I use them often” or “water parameters are good” they probably have the same API test kits from 2 years ago, and haven’t tested in weeks. Too bad so many in the hobby search for instant results.

    Andy–too frequent water change IMO. Any chance of heavy metal poisoning?

  • Andy…what are you water parameters? “perfect” means different things to different people.

  • Andy says:


    Thanks for getting back. My parameters have been very, very stable at:

    Calcium 420ppm
    Alkalinity 8.5dkh
    Magnesium 1400ppm

    Temp is kept to one degree of variation between 78-79

  • Andy…what are your NO3 and PO4 levels and what test kits are you using?

  • Andy says:


    Nitrates are undetectable, and I am using Red Sea and Elos kits for that.

    Phosphates are undetectable using Red Sea kits, and reads 0.02ppm on the Hanna checker…I actually just did this now.

  • Andy says:


    I am running the 250W Radium in a Lumenbright Mini reflector. I was running it 16″ off the water as manufacturer suggested. Some people said I should run it closer, but that just added heat and seemed to cause the flesh of the LPS to go translucent, revealing the skeleton underneath. I tried this a long time ago. Nonetheless, some people suggest the corals aren’t getting enough light, which I have a hard time believing. Raising the light just causes the light to go all over the room rather than the tank.

  • Kim says:

    Hi Andy,
    Reading your posts, I believe that you know what you are doing including test and change water every week; therefore, I won’t advise you what to do, but let you know what I have been doing because all my corals are healthy.

    I have Oceanic Biocube 29 gallons minus 30 pounds of live rock, and the remain is estimated about 20 gallons of water. I seldom feed my corals. Since I change 20% of water, which is 4 gallons, every two week, I don’t need a skimmer. I believe that using a skimmer, and change more than 20% of water every week will wide out all the good nutrition for the corals. Please don’t feel offended. This is my own opinion, and it works for me. Thanks everyone who takes the time to post and share your expertise.

  • Andy says:

    How could I be offended by that? Thanks for trying to help!

  • Monique says:

    Just a thought, how long are you mixing your saltwater for you water changes.

  • James says:

    Actually, it is helpful information. Basic common sense thing but something overlooked. Thanks for the reminder, Mark.
    It is a “quick tip”

  • Darren Thomas says:

    What trips me up is how do you know when to give up on a coral and remove it. When I first started this hobby I remember seeing a coral not doing so good and I’d get all freaked out, thinking if it dies it’ll foul up the whole works. Then I learned that corals can bounce back. Now Ive done a 180, and I end up leaving these half dead, sometimes only a speck of flesh left pieces that I hope will bounce back. Dont get me wrong my tanks is not full of half dead corals but I do have a couple of skeletons I should have let go way back.
    Any body else have trouble letting go?

  • Nicolas says:

    @Darren. I believe in the same thing. Sometimes I don’t always sit back and wait for the best. If it’s a coral I’ve had for years some of mine are about 8 maybe 9 years now. Those one’s suddenly have tissue lose, I’m talking crazy fast tissue loss. I immediately turn the lights off for a few days to see that they’re not reacting badly to the lighting, even if they’ve been under it for months/years.

    I do on ocassion do a heavy fraggin of the dead parts or separate the coral completely into frags and usually 2 of 5 of those frags survive. Again I find corals recover better away from strong lighting.

    I have a single deep water acro, purple, a beaut. It’s not doing well. It wasn’t enjoying the intense light. My other deep water acros love the light and color up amazingly. This one not so much. I am just watching it daily. I might give it an iodine dip for about 20min and remove the dead branches. May or may not work.

    The fact is not every coral likes the same conditions. Some thrive in my tank conditions others don’t. I don’t even have a squeeky clean tank. I have a good amount of N04 going on, good growth, good color, not Zeovit color but good enough. So as Mark said, you have to investigate a bit. Know your corals, know your fish behavior and think of what has changed recently. This can really help save them.

  • Brian says:

    Thanks for the tip Mark. As a newbie to the hobby, I had no idea corals would react to something that happened weeks prior. Love the shows and tips and thanks for keeping all levels of the hobby in mind as you make them. I’m sure this seems basic to those that have lots of experience, but us newbies have to learn too so we can one day reach that level of being an experienced reefer.

  • Kyle O says:

    Mark…….that was an awesome response to Klaas! Made me laugh out loud

    Thanks for all your efforts and the tons of “useful” information you share. You help out countless Reefers whether they admit it or not

  • Terri says:

    Sorry to hear you’re frustrated but don’t give up! You will succeed with this tank also. I’m guessing the corals are from your previous tank… Have the nutrients changed (NO3 & PO4)? What else may have changed since switching to a different tank (salt/salinity, calcium/alk supplement, food for fish/corals, flow, etc.)? You may find something there?! If your corals are large, they may need to be fragged to encourage healing and growth! They are kinda like humans/mammals in that they too grow old and slow down :0) My corals don’t grow as fast as I’d like (except zoas) and not as fast as alot of other reef tanks I watch. Every “tank” is different :0) Hang in there Andy!

  • Rich says:

    I know this sounds like a question you hear all the time, but I cant get rid of my cyano. Ive tried the 3 days of no light, I use dr smiths waste away for 2 weeks now. If anything I underfeed my fish. 180 tank, etss600 skimmer, dart gold return pump, 60″ ATI t5s, basically lps,softie tank,480 cal(alot of coraline) 8.7-9 alk, 1250 mag, 10 nit, .o2 phosphates, growth but salt biweekly35gal WC. This cyano keeps popping up. I have a korilia mag 6 +7 target feed my fungias elegance and acans,mt big colonie just slowly went from great to small polyps..Any ideas?

  • tony says:

    for major cyano problem is I would try bring in more current to the tank or changing light bulbs and make sure the alk is high

  • tony says:

    if your prostates are hi then it can slow coral growth up to 50 percent

  • tony says:


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