Hammer Coral

Close up of Hammer Coral Tentacles Green Tips

The Hammer coral gets its name from the hammer or anchor shape of its tentacles. During the day the tentacles are extended and provide nice movement to the reef which is much like the movement you would normally find only in soft corals. On top of the nice movement the tentacles fluoresce under actinic lighting adding vibrant color to the reef.  Hammer corals come in a variety of colors some of the most common are brown, purple tentacles with green tips, and green tentacles with pink tips.  Also found but a tad more rare are green tentacles with purple tips, orange tentacles, all purple, or a light peach color.


Common Names: Hammer Coral or Anchor Coral

Skill Level: Moderate

Classification: LPS

Disposition:  Aggressive

Light Level:  Moderate to High

Water Flow: Moderate

Water Conditions: 72-78° F, dKH 8-12, pH 8.1-8.4, sg 1.023-1.025


Hammer corals fluoresce under actinic lighting


Close up of Hammer Coral with purple tips

With Hammer corals it is especially important to realize that when the lights are off this coral will extend its sweeper tentacles. These tentacles can reach up to six inches long. Their purpose is to sting any corals which might be encroaching on its territory.  This is why you have to be careful with placement of this coral.  This trait is what classifies the coral as aggressive and it can deliver a very nasty sting to other corals.  The picture below is of a Green Pocillopora coral frag which was accidentally blown into a hammer coral frag. You can see that the hammer coral killed off any of Pocillopora it could touch.  The exception to this rule is that you can keep hammer corals in close proximity to corals of the same family such as frogspawn corals.

Pocillipora lost vs Hammer coral

Hammer corals are a photosynthetic coral and do not need to be directly fed. The coral produces its own food from the lights on your tank. However, you can feed your hammer coral and it will accept pieces of meaty foods by catching them in their tentacles.  Once a week I will shoot small pieces of shrimp into the tentacles of my hammer corals. I have noticed an improved growth rate when feeding the coral directly.

It has been my experience that too much flow will make the coral unhappy and the tentacles will not get full extension and this will give the coral an overall unhealthy look.  For this reason I would say that moderate water movement is best.  I have my Hammer coral placed in moderate lighting on the floor of my tank, but I have seen other reef tanks with the coral placed much higher and the coral still looked great. Moderate to High lighting is the correct lighting range


Hammer Coral Placement

Hammer coral propagation is handled like many other LPS corals. In the picture below you will see where this Hammer Coral is growing new heads. These will eventually grow into full heads and begin growing branches off the main stalk.  Use snips and break off heads from the main mother colony, break off the branches where they “fork”.  Once the piece is removed I glue it onto another piece of live rock or a frag plug. It’s okay to have your coral out of the water for several minutes.  Once the glue is dry place your rock back into the tank.  Give your coral several days before you see full polyp extension.

Notice the new heads growing off the main stalk of the coral



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44 thoughts on “Hammer Coral

  1. Hi, just a quick question I have bought a large hammer coral from a friend, I’ve placed on the sand at the bottom of my tank where it has been happy for a couple of weeks however I have started to notice tentacles dying off, my phosphates are at .25 , my calcium is slightly high and my oh was slightly low but I’ve added some buffered water, any ideas why they might be dying off?

    1. Hi,
      When you say tentacles dying off im not sure what that means. Do you mean they are not extending like they normally do or they are actually dying and falling off the coral? A large water change couldnt hurt since your phosphates are high. Have you changed anything in the last few weeks? New lights or changed / added a power head?

  2. My hammers tentacles close when my blue light comes on but then slowly come out again but look thin. The flow is medium with a medium movement. Is this ok I’ve had it for a week

    1. Hi Neil,
      To me this would indicate a few things. First off if the tentacles are retracting into the skeleton when the lights come on It might be you have the coral to close to the lights, I would lower it in your tank if possible. If your referring to the long stringy tentacles those are called sweeper tentacles and are usually out at night and are normal. If you mean ALL the tentacles appear to be long and stringy you might not have enough flow on your coral.
      Hope this helps and feel free to ask more questions or send me some pictures if you would like more info.

  3. Hi Tom,

    I have one hammer with a green tentacles and purple tips but the color is just not that vibrant. Any method of care to bring the neon vibrant color back? Tank is very clean undetectable po4/no3, LED lighting (radions) and the coral placement is fairly high.

    1. Hi Scott,
      A few quick questions. Was your hammer more colorful at one time and your saying it has begun to dull out? What is your LED spectrum set at, as in is it more white light than blue or are they 50-50?
      Something I think I would start with is trying to spot feed the coral. Its a popular theory that having undetectable nitrates and phosphates means the corals are literally starving and can look dull and not grow. So before fiddling with any lighting changes or moving the coral feeding it brings no risk to other corals and the hammer would probably appreciate it anyways. If you have access to them from a local pet store Id try some oyster eggs or even blend up a package of rods frozen fish food. Try doing this maybe 2-3 times a week for 2-3 weeks and lets see if the color changes.

  4. hi,
    my hammer coral is retreating back into its skeleton and when its out its only small tentecals and my clowns have hosted in him for about 2 months with no prob but now he is all closed up and he has been like that for a while now and i have a coralife biocube 29 gal stock lighting and stock pump and i was just wondering if anyone can help and he has about 16 heads so it would suck if i lost him.
    thanks cheryl.

    1. Hi Cheryl,
      Sorry to hear your having issues with your hammer coral. First thing I would start with is some water tests mainly your salt levels and nitrate levels. If you don’t have these tests do you have a local reef store that you could have test your water? Also what type of lighting do you have on your tank. I know you said stock but does that mean a metal halide or leds?
      Another thing to think about , have you changed anything from the time the coral looked happy till now? Such as coral location, changing lightbulbs, or adding power heads or anything like that?
      Thanks and look forward to hearing from you.

  5. Hi Tom,

    I have several Hammers and one frogspawn in my tank (125g), about two weeks ago I noticed a few new heads on one of my large Hammers, Yay!!!!!!!

    in the last couple of days the new heads started dying off 🙁 and now it has transferred to some of the larger heads. this morning I cut off the dead and dying heads.

    its a 2 year old tank with very few issues over the time, the only other real issue was a few months back where my torches started dying off??

    my parameters are fairly stable (Ca, mg, kh etc) so wondering what you think I should look for

    1. Hi Rick,
      My first thought is you had an alk swing, are you sure it’s been stable? Have you moved changed anything recently such as power head placement or temperature? Have you tested ph lately? I would start with ph testing and alk testing . Let me know your results.

  6. Hi all my hammer has started to detach from the skeleton . There is now a piece on the sand bed why is this happening

    1. Hi Niel,
      A lot of people refer to this as polyp bailout. It’s a sign your coral is very stressed. Do you have any test kits to test your water and let us know the results? I would focus mainly on alk, ph, and phosphates to start.

  7. Hi my readings using a king British 6 in 1 test is
    Ph. 6.8
    Kh mg/1, 50
    gh mg/1, 250
    Nitrate, 0
    Nitrite, 0
    Not sure how this reads.

    1. Hi Niel,
      First off to me thats some low PH.
      Are you running a calc reactor? The Ph coudl very easily be causing stress to your corals.
      I would look into some PH buffer and try raising that slowly to 8.2.

  8. My hammer coral not opening up since 5 to 6 days. Water quality is good, temperature is at 27°C, I don’t know what happened. Please help.

    1. Hello,
      Sorry to hear you are having issues. Has anything changed in your tank like running new carbon or new lights? If not my first guess would be your salinity might be off. Have you checked that recently?

  9. Hi. My hammer coral seems to be dropping off the tentacle parts. They remain on the bottom of the tank and one in a rock crevice and continue alive ?? Everything I have read does not mention this – should I leave the dropped off bits in the tank or remove them?

    1. Yes you can leave them in your tank and they should begin regrowing their skeleton and forming new colonies as long as your water is stable. This is normally a sign that your coral is very stressed, have you checked your parameters lately?

  10. Yes, water is great, no issues that I can find so not sure why it is stressed. Everything else is growing well and looks very healthy. Thanks so much for your help.

  11. hi i have just bought a hammer coral at the shop it looked great it retracted into its skeleton while transporting home i put it in my tank but it has not come out again it has been about two weeks

    1. Hi brandon,
      Sorry it was so long for me to reply i have been out of the country.
      If the coral has never extended since the store I would first check your water params, especially your salt.
      If that all is in good order the next thing i would look at is too much flow or too much light.
      Moving to a lower light or flow could help the coral begin to extend.
      How has the coral been since you wrote your comment?

  12. I have three hammer corals one of them with 4 heads doing great but the other two there tentacles stay In the skeleton no extension at all using led lights all other coral look good
    Params seem fine but ph stays around 8.7 -8.8 can’t get it to go lower alk. Is around 11 cal 420 salinity 1.026 any ideas why just two are acting like this even put them by the open one did not help phos around 0 nitrate 0-5 hard to tell the color on test

    1. Are the two that are closed in a higher flow or light than the one which is open? While all of 11 is okayish, I find that the higher all is that corals can be more sensative to light. I would try moving the corals into less light / flow and see what happens.

  13. I know this comment section hasn’t been active in awhile, but I’m worried about my hammer. No polyps have dropped off, and while some of the skeleton was calcified in the LFS w, it seemed to be happy hen I brought it home for about a week with full extensions within 2 hours of placement, and everyday since….

    Now? He still opens, and extends his polyps. Its just that his polyps are over extending, or ‘drooping’. Almost like elastic bands that have been overstretched. He still responds/retracts when something brushes a polyp. No polyps have detached at all…. His colouring still looks good.

    I tested the water yesterday, and all parameters are literally ideal (I’ve been doing partial water changes since I noticed a few days ago). Phos/Amm/Nits = 0, Ca = 400, sal = 1.025. I have it reasonably high in my 20 gallon tank with 3x8watt IM LED lights with protein skimmer and IM filtrationx2. Tank was torn down and reconfigured 3 months ago, and corals re-added after the parameters were stable again (they were stored in LFS while the tank re-cycled). I bought him and put him in when my original corals were settled and happy and fully stable (and I had spare $).

    The tank has a bubble tip anemone, a frogspawn, kenya tree, a bunch of different types of star polyps, and a Fungia plate coral, some zoas, and a dendro colony – all of which are very very very happy! I have some snails as well, but thats about it. I have taken care to keep the hammer away from everything but the significantly smaller frogspawn (frogspawn polyps are no longer than 3/4″, and it is 4.5″ away). There are no marks on it as if it had been stung by the frogspawn.

    I have no fish (yet). Stabilising my corals before I add more livestock.

    Am I just being paranoid? Or is there something like temperature (81) or flow (indirect, high to moderate) that is causing it to droop? Is drooping even a cause for concern?


    ps. I may have included too much information, but more is always good… right? 🙂

    1. Too much info is always a good thing =]
      If the tentacles are extended that means that the coral senses food in the water. Which is totally fine, you could even softly shoot some thawed out frozen brine shrimp to have good growth. I would assume the tentacles seem droopy because they are in low flow. If the coral appears happy I wouldnt move it just because of that though. Let me know how it goes!

  14. I just bought a small hammer and stuck its bone part into a hole in my live rock and used epoxy around it so the crabs wouldn’t knock it out. Now I am worried the bone part wont have room to grow. Not sure really how the bone grows, up? out? The fleshy part is fully out and the tentacles are happy.

    1. The skeleton will grow out of the hole you placed it. Then when it has room it will developed new branches with tentacles. It should like to me you did fine =]
      Good luck with your hammer.

  15. hi,

    by impulse i bought a hammer coral without do my research..
    i know… shame on me…
    my Ca, Mg and Kh are low (330, 1130, 6.7)
    how long can i keep the hammer inthose conditions ?

    should i be ok to raise those levels during several weeks or it will be too late

    thanks for the help

  16. Hello~
    I’ve had a hammer for about 3 years, it’s been doing very well growing from 2 branches to 8. I’ve just notiiced one of the smaller/lower ones is dying/dead the area around the skeleton is rough and the soft tenticals are gone. My question is should I cut this part off or leave it? Will the polyp come back if I leave it?
    I fear a movement of one of the power heads flow was too high for the younger branches and it killed it.
    The level are all “acceptable”, according to the strip tests I use. With the acception of KH a bit too low at 120.
    Salinity at 1.022
    Thanks for your time,

  17. hey I bought an atomic hammer a really big specimen with tissue all the way down the skeleton looked really awesome in lfs acclimated it for about 30 mins at home and placed about 4 to 5 inches off my substrate. I have acroporas so my flow is higher but I put it in a lower flow spot.Tthe next day I come home from work and half the colony has polyp bailout all my params are in check I don’t know what happened I moved it again to a place where there is minimal flow and it seems to be doing better but should I frag off the healthy half from the non healthy half or should I just leave it alone

  18. We have set up our first marine tank. We have a green hammer torch that we got a few weeks ago after our tank had stabilised for about a month, the idea being it would be a nice altetnative to an anemone for our cliwn fish. The tentacles are extending to about 1-2 inchrs during thecday when the lights are on but when the blue lights kick in, the tentacles retract almost completely… is this normal?

  19. My green hammer coral has had heads dying. Now I have 4 heads left and on 2 heads the tentacles had started to retract into the skeleton no matter what time of the day. I don’t know what to do anymore; I have tried Coral Frenzy and Kent supplements. It is in the middle of my tank with T5 HO lamps and nitrates, nitrite, and ammonia are all good.

  20. Hi Sir. I have bought a branched hammer coral. One of the branches lost her soft tissue and tentacles but others are ok. Is there any chance to recover?

    1. Hello, I would snip off the branch which lost it’s soft tissue and tentacles.
      You can try moving it to a lower flow portion of the tank, however once you lose most of the tissue it is a pretty safe bet it will not recover but no harm in trying!
      I would leave the rest of the colony where it is though.

  21. I have Hammer Coral (purple / green) two of the soft issue tentacle have detached from the base and are floating the around in the tank. I thought they would die, BUT it’s been 3 days and they look good, as when they where on the base. I have tried to put them on a rock cove, hoping they would attach, but they keep moving due to flow.
    1. Is this normal and is there hope they will attach and survive.
    2. I still have 2 good heads on the base coal and 3 empty heads, should I cut them off, or just leave them? (there is space between heads )

    This is my first salt water tank so any advice is good to me..
    Thank you

  22. I have a hammer coral one small head died now a bigger head is starting 2 show skeleton water is ok just did water change I have recently added a powerhead and purigen & bio chem as I have a leather coral in the same tank.

  23. Question on wall hammers.
    Been about four days since i got one. Third time over last 2. Years. He was opening up but has been rather retracted last few days. He is higher in the tank but just as high as the green brAnching coral whoch i bpught same time. Under kessil lighting in 75 gallon. Everuthing else in tank is coming out fine. Nitrates around 5. Phosphate close to 0. 8.0 ph. 80 degrees. 1.023 to 24 salinity. The return flow is right above it but it is not in direct flow. I did a weekly water chsnge. Maybe that irked it. No signs of brown jelly. Have seen a floating polyp once. A small one. Areas around edge seem to be a little more out. But most is retratced as compared to first 3 days. Thoughts. Placements? Actions to be taken?

  24. I have a hammer Coral that has been great for over 8 months. A week ago it closed up and hasn’t opened since. No new corals around it. Water tested shows salinity 1.026, nitrates .25, ph 8.3, alk 11, calcium 440. It’s been in an area of moderate to low flow and at bottom of tank in the sand.

  25. Any advice on keeping hammer coral with sea horse? Specifically, if this coral seeks to sting other coral, are fish/sea horses safe with it?

    1. I have never kept a sea horse, it’s my understanding though that they need low flow.
      I dont think that a hammer coral would be happy in such a low flow tank.
      However this is just my speculation and am not sure one way or the other.
      Sorry I couldnt help!

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