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Live sand question


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This might be a silly question but I can't figure it out.


I just started my first tank. I added already cured live rock and tested the water about a week later. Ammonia and nitrites are zero. Nitrate, around 10ppm. I'm assuming this means my tank has cycled.


I want to had some live sand, but I'm concerned. In theory, adding live sand will add more bacteria. However, since my ammonia and nitrites are zero, they will have nothing to "eat".


Wouldn't this cause a dying off of some of the bacteria (too many & not enough food) which would give me an ammonia spike, which would once again feed the bacteria and create a new equilibrium?


I want to add sand, but I don't want to go "backward" and have to wait to cycle my tank again. What should my next step be? Should I "feed" the sand when I add it to prevent any die-off? Am I off base in making that assumption of die off in the first place? Is this all just part of establishing a new tank? Any guidance would be appreciated. Thanks

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If you want the sand, I think you're going to have to wait for the cycle again.


I can't think of any way to not have it do ANY cycle. If you put it in a bucket outside the tank, let it go for a week or two with maybe a shrimp (from a supermarket, dead and decaying, to produce ammonia) in the bucket, and then pull the shrimp, dump the water down the drain, and move the sand. This would be equivalent to curing the sand. You could also buy cured sand, which would have the same effect...but even a short move from the LFS to your home, or from the bucket to the main tank, will result in a little bit of die-off as a new equilibrium is established. Hence, I think you'll have to wait.


That said, it'll probably be a pretty short wait. You'll have a spike that will very quickly go to nitrates, simply because you've already got established bacterial colonies in your tank. Keep in mind that the doubling time for many bacteria is ~20 minutes to an hour under ideal conditions (plenty of "food" available, in this case this would be ammonia) so if you get a spike, you're going to see bacteria reproducing like crazy to get rid of it.


There's a concept in population biology called the exponential growth curve that's used to model resource-unlimited populations, specifically populations with very large numbers of individuals that reproduce in a pattern where one divides into two (e.g. bacteria)....not sure if you're familiar, but basically it dictates that you'll get a slow rate of climb at the beginning, but the more you have the quicker you can make more. This is because on your second generation you've got 2 bacteria, each of which divides into 2....so


2*2 = 4 you got two new ones in twenty minutes.


But twenty five generations later,


2*2^25 = 2*33554432 = 2^26 = 67108864 so you got 33554432 new ones in that same 20 minutes.


Hence, once you've got some bacteria in your tank, you can make more bacteria hella fast, which means you don't need to worry too much about mini-cycles.


You probably won't need to feed the sand. The die-off of some of its bacteria will, as you said, create some ammonia for the rest to feed off of. Just remember how fast bacteria double and don't worry too much about it.



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Very informative! Thanks much!


One other thing, am I correct in my thinking that the "marker" for my tank being cycled is when only nitrate is detectable (and less than 10ppm) or is it when nothing is detectable? Getting 2 differant answers from LFS. I know there are bacteria that convert nitrate to Nitrogen gas, but I heard they are slow growing anerobes and show up later. Can't I just do a partial water change to lower the nitrates or do I have to wait untll all bacterial flora are up and running?


In other words, what consitutes an offical cycle?

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In reef systems, nitrates are very hard to get rid of any way except through water changes. You're right that there are nitrogen-fixing anaerobes, but anaerobes can't find much of a home in reef systems, what with there being dissolved oxygen everywhere. If you have a deep sand bed, they'll happilly grow under the sand, but otherwise I don't see it happening.


Hence your cycle is complete when nitrates spike. Do a big water change at that point and you should be good to go.



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Blind Tree Frog

I wouldn't think that adding live sand would cause enough of a problem that you'd have to worry about it in a cycled tank. You've already got bacteria working away to convert ammonia to nitrogen and you've got stuff dying and creating ammonia for you already (it just gets processed out before it's noticable). So while adding the live sand might create a small ammonia bump while things starve (lots of bacteria, not a lot of food), the bump would be very low and short i would think.


But I'm still learning.

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if the live sand you purchase is cycled at most you'll have a very small spike which your lr should be able to handle. don't think that you have to do something as drastic with the shirmp as ugly recommends. bacteria will migrate or start growing on the sand eventually.

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Wee-Reef Master

I concur w/ Blind Tree Frog. I believe that there won't be a significant problem. I think that any spike you experience will be minimal, at most.....you may not even notice it at best. Presumably, if the sand is truly live, there is quite a bit less die-off than live rock as there are no substantial organisms decomposing as is the case with live rock. Good luck!

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Thanks all. Very helpful! I put the live sand in tonight. Look for posts from me in the inverts forum. Will need help with the composition of my clean up crew. That goes in next.


P.S. I'm uploading images of my progress in the members gallery section. Check it out

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