Terrible Advice Tuesdays (T.A.Tues): The Foolproof Way To Crash Your Saltwater Tank


Terrible Advice Tuesdays (T.A.Tues): If you stop carbon dosing your tank, it will crash.

The rest of the story: Did you know that the end of the world is coming too?!

Let’s break this terrible advice down piece by piece.

First, when I think of a tank crashing, I think of a wide loss of fish and coral life within 72 hours.

Second, carbon dosing involves adding a carbon source to grow heterotrophic bacteria. These bacteria uptake phosphates and nitrates among other nutrients. (Note that heterotrophic bacteria are completely different from nitrifying bacteria. Also note that running activated carbon in your tank is NOT carbon dosing). The nutrient-rich bacteria is then exported from your tank usually via protein skimming. Over time, enough bacteria can be grown that your tank reaches a low nutrient or ultra-low (ULN) state where nitrates and phosphates are low enough that your test kit won’t detect them. Vodka dosing, biopellets and the Zeovit system are all examples of carbon dosing as discussed in my algae guide.

If you were to suddenly stop carbon dosing your tank, heterotrophic bacteria counts would drop and nutrient levels (nitrates and phosphates) would rise. How much will the nutrient levels rise? That will depend on lots of factors such as age of the tank, bioload levels, filtration on the tank, etc and an exact rise is impossible to calculate. Also, the bacteria counts will drop off slowly such that you could easily track the rise in nutrient levels and react to the situation.

A large rise in nitrate and phosphate levels would likely annoy and potentially kill your small-polyped stony (SPS) corals but it would take weeks not days. However, your large-polyp stony (LPS) corals and soft corals would probably celebrate that there was “junk” in the water and might look better after you stop carbon dosing!

What would your fish think about you stopping carbon dosing? They will care less.

And if your tank crashes immediately after you stop carbon dosing, something else was wrong.

If you are carbon dosing your tank and want to stop, do it slowly over the course of a month or more. As I’ve said lots of times before, saltwater tanks are like grumpy old men. They don’t want to change and if they do have to change, they want to do it slowly.

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Comments for this article (18)

  • Dave says:

    That is some great advice you don’t hear everyday an thad or even consider. Thanks for the advice.

  • Chris says:

    Hey Mark,

    What’s your opinion on starting to use bio pellets to be safe if I currently have undetectable nitrates and in most checks .02 or less of phosphates. I was thinking of doing about the 1/4 amount of recommended dose. Im I just gonna be wasting my time

  • Chris..if your levels are already that low, I doubt you’d see much of a difference running pellets.

  • JasPR says:

    It often becomes obvious that some hobbyists have way way too much time on their hands. Don’t get me wrong, I admire those that dig deep to truly understand their aquarium’s dynamic. Its a huge advantage to have a brad perspective on the ‘normal’ status of aquarium water and ecosystem when something goes ‘off’.
    BUT as is human nature, we often look for ghosts and boogie men that simply are not there. The first sign of this hobbyists syndrome is to take a real scientific and exaggerate it to the extreme.
    in this case, just TRY and stop bacteria from growing- I dare you! 🙂 indeed, the normal cycle of a closed system is one where we battle heterotrophic forms so as to allow autotrophic forms and opportunity to establish ( something that causes a new tank syndrome to persist). Dosing to encourage heterotrophic forms is a bandaid solution to a much greater problem. Period. JasPR

  • Nikolaus says:

    Here is an interesting one for you. 0 nitrates and 0 phosphates is actually a bad thing. Corals colors come from photosynthetic algae, called zooxanthellae. Algae uses N and P. if you reduce the n and p to true 0 the corals fade and bleach. having some n and p makes the coral look bettter than none at all.

  • JasPR says:

    very interesting point Niko and also right to the heart of it– we all tend to, at some point in the learning curve, take bits of scientific truths to an extreme. True zero , by the way, is also probably impossible in closed systems– ‘unmeasurable’ is probably more accurate ( agreed?)
    I think one of the true ‘ epiphany’ moments comes when one learns to sort out the differences and impossibilities when comparing real ocean conditions and dynamics with that of our closed systems.

  • Carl Cliche says:

    But, is not everything we do a “Bandaid” to a much bigger problem. If you follow that logic, water changes are a bandaid. What about protein skimming, activated carbon, gfo and dosing are they all not baindaids? I just had an ‘epiphany’. We should all just cut the bottoms out of our tanks and place them out on some reefs so we can match real ocean conditions.

  • Nikolaus says:

    Not sure where that came from Carl. The hobby is a delicate dance. Trying to maintain a series of chemical reactions. While some go for bandaids, others try to find a good balance of natural and man made changes to maintain the system. The difference is we use an enclosed system that is not fully capable of maintaining the natural homeostasis without intervention.

  • Merne says:

    Well that would be no fun. I don’t think of these things as bandaids. We don’t really try to match ocean conditions, so much as match proven husbandry techniques and levels. I don’t think the main goal is to match all ocean conditions in our boxes.

  • Nikolaus says:

    Well said. We strive for growth and color, not natural conditions. If we wanted to mimmic nature no one would ask if a fish was reef safe, and growth would be a fraction of what it is now. In nature parrotfish eat coral, not pellets.

  • Carl Cliche says:

    I agree with you Nikolaus and Merne. By trying these various techniques such as bio-pellets we try to improve the conditions of our tanks and advance the technology in general. There are lot’s of ways to achieve our goals and my point was we should not refer to any technique as a “bandaid”. If someone wants to try one of these techniques we should encourage and anxiously await results. Sorry if I overreacted to someone else’s post.

  • Mark says:

    Well, I for one have experienced this loss of coral from stopping carbon dosing. I was scheduled for surgery and knew I would not be able to do water changes and other husbandry rituals after my surgery. So the night before I tried to complete a major cleaning on all my equipment. Unfortunately, I wasn’t able to complete the needed cleaning on the bio-pellet reactor and left it off the system thinking I would be able to get to it after the surgery. That cleaning never happened. I lost several SPS and a few LPS. Definately head Mark’s advice to reduce the carbon dosing slowly over time.

  • JasPR says:

    stability is as important as a base or set point. A turn pH crash is pretty rare in a properly stocked tank. And alkaline reserve is impressive in aquariums with routine water changes. IMHO of course.

    As for new discoveries revolutionizing the hobby— nature, natural biological events ( cycling, CO2 system etc)– they haven’t changed since the B.C. era! 🙂 EVERY closed system is ruled by a half a dozen biological realities and a few spin off predictable events from those basic biochemical reactions. ALL the rest is subtext. We have to be careful not to fall into the trap that marine systems are somehow technology systems. Tech can help and approach the realities of biological metabolisms in clever ways– but they don’t change evolution or ecosystem realities. And as mentioned, at worst they can be administered as bandaids to patch over weakness in other parts of the natural cycle.
    Closed systems are nutrient driven and as eutrophication trend models that are slaves to deterioration. No one has come up with a better ‘technology’ for balance and reset of base line readings than water changes. The rest simply buys time and short term remedies. In short there is no perpetual motion machines in a closed system and not even ‘Apple’ will create one in our life times.
    The marine hobby in the hands of amateurs is only 65 or so years old.
    the fundamental model then was a ‘mild’ nitrification system within a closed container. Today it is a mild and remote nitrification system. what we have learned is to control the EXTENT of heterotrophic and anaerobic activities. Simple is sophisticated. Complex is an illusion of sophisticated. But chasing the dragon IS fun. 🙂 Peace, JasPR

  • JasonandSarah says:

    first off jasPR have you been reading to many C future philosophy books? lol jk obviously your very knowledgeable in marine life in a closed system. but I think like always you go a little beyond the point that’s taking place, now if you disagree with carbon dosing then that’s your opinion and you deserve your opinion. but so does Mark and Carl if they like the idea of carbon dosing! I’m no scientist but I do firmly believe that the greatest part of this hobby is that nobody has to do things an exact way to be successful!
    Now I’m sure you’ve done more research and studies then allot of us have ever thought of but do you have any factual evidence on why carbon dosing is just a “bandaid”? or could it be just another part of the reef tank routines that can be an option? if someone carbon doses continually and has great results and never has any problems ( like allot of people do now a days) how can that be a bandaid and not a fix? I mean are you a 100% positive there isn’t any kind of natural carbon dosing in the ocean?
    I’m in no way an expert on any of this but I do have a very successful reef tank (without carbon dosing) and I just don’t think it’s right to dismiss every new idea because it’s been working a different way for years. especially without factual evidence of how and why it’s not good for our reef tanks?
    Learning from the past is great! creating the future from what you’ve leaned from the past is INNOVATION

  • Daniel Gappa says:

    Does this mean that [No man may know the hour of the tank crash]??

  • Rick Baker says:

    what if you don’t use carbon to begin with?

  • Erick Sundeen says:

    Always remember there are pros and cons for everything in life. You can never please or achieve 100% of anything, but striving to do so makes us human. Everyone has there own opinion. So remember “fish are friends, not food” so know your tank and prevent the crash. Don’t wait for it.

  • Jay Jay says:

    Firstly, I know this is an old post..

    I have recently started carbon dosing, and came across this thread while researching, and IMO I do agree this is a “bandaid”, as is eveything we do to our systems. Simply because it would be impossible to find a permanent ‘fix’ within a closed system. Fundamentally, this is a hobby, and part of the joy of the hobby is maintaining the system. I for one love applying my “bandaids” at the weekends, be it water changes, adding salt, producing RO, carbon dosing, skimming etc etc etc.

    At the end of the day; if you can’t please everyone.. please yourself.

    Find what works for you and enjoy it.

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