Terrible Advice Tuesdays (T.A.Tues): 3 Days of No Lights = Coral Death

Terrible Advice Tuesdays (T.A.Tues): 3 days of darkness will harm your corals

The rest of the story: 3 days of darkness is a method used to control nuisance algae. The idea behind it is simple: without light, algae dies. Also simple is how you perform 3 days of darkness: just turn your lights off for 3 days.

Once you turn the lights back on, you’ll be amazed to find that your corals are perfectly fine! Think about it: out on the reefs in the ocean is it a perfectly sunny day 365 days a year?

No. There are plenty of days when the sun doesn’t shine and sometimes doesn’t shine for days on end. Your corals can handle the 3 days of darkness no sweat. Of course if you have a coral that is dying then the 3 days of darkness might do it in and if it doesn’t survive 3 days of darkness, it probably wasn’t going to make it anyway.

And as a precaution I recommend you ramp up your photoperiod once you turn your lights back on. Probably not needed and it doesn’t hurt to be safe.

Finally, if you are relying solely on 3 days of darkness to fix your algae problem, here’s some bad news for you: the algae is going to come back sooner or later because you haven’t fixed the underlying issue on why you have an algae problem. 3 days of darkness can be part of the solution for fixing an algae outbreak, but it is not a lasting solution.


Browse the Store! Questions?

Comments for this article (38)

  • Jason says:

    Since buying your “The No-Nonsense Guide To Preventing and Curing Nuisance Algae Outbreaks” I haven’t had any more algae problems.

  • Jason…thanks for the feedback and I’m glad to hear algae is a thing of the past in your tank!

  • Tony says:

    One thing you can’t beat good husbandry and regular PM plus GFO REACTOR. And get some fish that love
    Algae. That’s my take, mind you I am still new to the hobby.

  • Andrew Levin says:

    Hey Mark,

    It is so funny you sent this algae fix out today, as I am now in the midst of a major hair algae problem in my 29 Biocube. Even though I have Emerald Crabs, a Protein Skimmer, UV Sterilizer, and my water chemistry is perfect. I also will be ordering your guide on this, along with most of the others. Thanks for all the informative Terrible Advice Tuesdays, and Friday am Quick Tips. I always look frward to these.

    See you August at MACNA,
    Andrew Levin

  • Chris says:

    I bought your guide on the subject as well and loved every minute of it.
    I typically just use three days of darkness any time I go on a long weekend – it reduces my evaporation to zero, and gives everything a rest.

  • Chris…interesting idea on preventing evaporation. Are you running LEDs over your tank?

  • Tron says:

    Does it matter if the tankis sitting in a room that has windows letting in some natural light? Will this still work,or will the natural light allow the algae to “hang on” over the 3 days?

  • Bryan says:

    What do you do about fish feeding during the three days of darkness? My fish hide in the rocks and will not feed when the lights are out. I have your guide on algae control and used the 3 days of darkness. I just turned the lights on briefly during feeding and then turned them back off. I am not sure if this was counter productive when it comes to the algae control though. My algae problem was cured after folllowing a number of suggestions in the guide.

  • Alessandro says:

    Hi Mark,

    does the “three days of night” method work with macroalgae (I guess not..)? I have a big problem of caulerpa serrulata and I am getting sick of trying to eradicate it manually. Would your guide shed some light on my issue?

    thank you

  • Alessandro…caulperpa is tough stuff. The 3 days of darkness might weaken it such that it would help with manual removal. However, I doubt that 3 days of darkness will eradicate it.

  • Bryan…I do what you do…turn the lights on for 10 mins or so such that the fish come out from hiding. I feed then turn the lights back off.

  • Tron…if there is a lot of natural light entering the room, I’d block out that light either by blocking out the windows or putting a sheet around your tank. If you put a sheet around your tank then make sure you leave the top open for gas exchange.

  • mardaman says:

    When doing the 3 days of darkness, should I leave the UV Sterilizer on?

  • JasPR says:

    Good Morning! BRIGHT and SUNNY good morning! 🙂 Let me start out by saying, I’m not an expert on the fine points of art associated with full blown hard coral reef keeping at the high end of that art form!
    But I do fancy myself as something of an expert on aquarium science! 🙂
    Algae is a ‘condition’ of a living system. A condition of a living system. It is ALWAYS present in potential. The idea is to crowd it out and keep it humble . How? simple- do two things– do not provide it with the luxury elements needed to do well and 2) crowd it out by encouraging other species that use the rare luxury nutrients needed by both species. and favor the desired species over the undesirable species. you CAN’T starve out all algae of you will also kill many valuable forms within inverts. And once you return the lights to a normal photo-period and intensity, if you have not remedied the conditions, algae will return with a fury as you have created a void space for it to fill like a wild fire!
    Many clever tricks have been devised over the years to favor desirable species and starve out and ‘make prey’ undesirable species– none are a perfect answer. But in aggregate, employed together with a step up in water changes and maintenance, you can get an amazing synergy and an end to slime algae ( bacteria), string algae and many of the problematic higher algae forms ( bubble for instance). JasPR

  • JasPR says:

    definite suggestion! keep your protein skimmer on if you attempt to kill off algae! ALL that carbon breakdown and all of internal fluid and its stored luxury content will dump into your water column! You absolutely need to pull it out. The way algae works is it takes material out of the water to fuel photosynthesis. Some materials needed are common in closed systems and others are limited in ratio. many of the species we see as common are able to store up some of those rare elements for future use. And they need these rare ingredients to build a complete photosynthetic model. Think of this as a factory building a car– to make a complete car it needs tires. And if tires are rare, it can’t complete the car. But if it stores up a supply of these rare tires it will be able to build enough cars to meet demand.
    SO when we kill off algae in a mass way such as disrupting photosynthesis will a lack of light, the cells will leach out all their contents as they die. This, ironically, puts some very rare and valuable ‘tires’ back into circulation– enough to fuel future generations of string, bubble and other filamentous algae forms. Ironically, you are adding rare fertilizer to the water column. Sooo if you limit your big picture vision to ‘ algae bad- me kill’ type of aquarium keep, you will need to get the component ingredients for mass photosynthesis OUT of the system– skimming and water changes are the only remedy ( so please don’t add chemicals to try and cope with this reality). For what its worth, JasPR

  • Mr Saltwater a need your counsel, my house has inputs sun everywhere, the roof is glass and I can not do anything, that gives me a lot of seaweed, which I can do????

  • Mark says:

    I typically do a good size water change after 3 days of darkness. Worked like a charm.

  • I just sent you an email willian

  • Steve Dodd says:

    hi Mark , regarding three days of darkness , would this harm a big carpet anemone

  • Steve Dodd…anemones won’t be affected by the 3 days of darkness. They likely won’t inflate fully during the darkness and some might move to a new home. Most of my anemones have stayed put through the 3 days of darkness

  • Edward Claxton says:

    Mr.saltwater tank,
    This is kinda on topic on the nuisance algae promblems
    I have a 125 with an outbreak of brown slim thats whay it looks like anyways. Its stringy and has bubbles kinda of like red slime but brown. Ive had it since February and everything seemed fine I had my cycle the normal diatoms then everything cleaned up and now my tank has slowly started to become a mess. I watched a video of you helpimg a friens it was a two video series. He had red slime you showed him about gfo rreactor and its media and ran it for a week I think he even did the 3 days of darkness. Ive had gfo in my reactor about april right around my cycle started to end and my chemistry started to stablize. I change the media once a month. I also add 12 teaspoons to my bulk reef supply dual reactor. Is this the right amount can to much harm your tank? It said on instructions 1 teaspoon for every 10 gallons and for carbon 1 teaspoon for every 4 gallons. My test kit I believe is giving me false readingbc its says I have no phosphates but I am using the API kit in which I hate. The good news I just ordered the hanna checker for phosphates yesterday. Im starting my own kit from your mixed reef list. Im also going to try rowaphos in my gfo reactor what do you thibk of this stuff? By the way I do have a refgium with a ins reef dynamics 135 skimmer I run dry. I have 2 filter socks from brs I change every 3 to 4 days. And a refugium chamber with cheato in it, but its slowly dieing. This tells me from watching some of yours and vividaquariums videos that the phosphates are get used up by the algae so and the rest by gfo if there is any left and none for my cheato. What would you recommend me do? Thanks

  • Margaret says:

    How would 3 days of darkness effect clams?

  • Margaret…a healthy clam won’t be affected by 3 days of darkness

  • mike B. says:

    I have a big problem with dinoflagelates in my 180 reef. Run 3 250 halides. Finally turned lights off for 3 days, changed the GFO, had a big skimmer working, and it came back in a couple weeks. Have about 8 fish, don’t feed them much, and have been using a small hose with toothbrush attached to vacume rock and pick up the dino’s.

    Maybe more frequent water changes? Doing about 1xper 3 or 4 weeks.

    And how often should I replace GFO? Thx. Mike

  • Bary says:

    I know it’s not the ideal solution and can bring an entire set of other issues; but another way to combat hair and many other types of algae is by cautious use of a Sea Hare. I had the same situation as many; great chemistry but something not right. Hair algae was winning the battle until I introduced a Sea Hare. He cleaned it up in two days and is loving life with occasional feedings of freeze dried sheet algae. Little guy knows right where I clip the holder and eagerly climbs to it within minutes. I have to say this guy is more entertaining than many other aspects of my tank. Looks like a slow moving marine version of Shrek!

  • Greg Mitchell says:

    Can I buy your books in the U.K

  • Rick says:

    I had a horrible hair algae outbreak about a month ago due to a phosphate spike. bought a Tomini tang and he wiped out all the algae in 3 days!! problem is, I still can’t fix the phosphate issue!! Mark do you have any other suggestions besides water changes? those aren’t helping?
    cost is not an issue to get rid of this problem!! 🙁

  • Greg Mitchell…sent you an email

  • Rick…there is lots of places to look for phosphate issues such as dirty filters, detritus build up, over feeding, over stocked tank, etc. Also, make sure your test kit is one that is reliable. Here’s my recommended test kit list for you

  • bill sawyer says:

    mark, need to know if tiny white star fish are good or bad to have in my 180 gal. tank.. they are smaller then on eraser head…they appear to eat the small amounts of algae off the glass.. i have what apears to be 100s of them all over the glass and more likely on the live rock as well, they hitch hiked in something.. they are easy removed by siphoning… but are they freind or fo .. bill

  • Mike says:

    Hello Mark:
    I consider myself a REEF ENTHUSIAST because I keep my spending in check, but still want coral. I am re-starting my 180 gal (slow water drip attacked my wood floors).
    I like your approach to salt water care, and slowly getting through the archives of information you provide.
    Keep up the good work.
    P.S love the T-shirts

  • Victoria Monita says:

    I have green water for a week now and and noticed my fish has white spots …what do I do??? Help!!

  • Victoria Monita says:

    O yea ibhave saltwater tank w/ green water and white spots on my fish

  • Rich says:

    Hello Mark,

    I’d like to give the 3 days of darkness a shot. That being said my reef tank holds a large maxima clam and I’m not sure how he’d react to zero light for 3 days. Please help. Thanks in advance:)

  • Rich…the clam will be fine.

  • Tom says:

    Been battling Dino’s. Did a bacteria bomb, peroxide etc… No luck. Trying 3 day blackout. What’s your secret weapon for Dino’s??


  • Thomas Herndon says:

    I have a few fish, a CUC and live rock in a 40gal aquarium. My bulbs keep blowing and I’m wondering how long I can go with no artificial light. I’m considering upgrading my aquarium to a 75gal anyway. Btw, just discovered your YouTube channel, and I’ve been binge watching.

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.