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Can I remove half of my rock?

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My livestock is:

2 clowns

2 pompom crabs

1 porcelain crab

Misc snails

Misc zoas


So I feel like I have way too much rock in my tank.  I have a 16 gallon AIO and the display area is 12 gallons.  The tank is around 8 months old.  When I set it up I used 18lbs of dry rock and it is just too much.  I have trouble with flow around it and it is hard to clean because it takes up so much space in the display.  I'm having some algae issues because of it. 


I have a new fusion 20 I am going to be setting in place of the 16 so I want to clean the rocks and kind of start over.  No bleach or acid wash, just a good scrub and limited light to get rid of the hair algae before it goes in the new setup.


So my plan is to remove about half of it.  Scrub the rocks I remove with some peroxide, then put them in a bucket with new water circulating and limited ambient light for about 2 weeks.  When I set up the new tank I will use the clean rocks to start and do the same 2 week cleaning on the rest of the rock before it goes in.


Does this sound like a good plan or is there a better way to go about this? 

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It depends on a bunch of things. How porous is your rock? Do you have any other bio media?


clowns create lots of n



I am using under 5 pounds of stax  rock in my 13 with one clown which probably is not enough for the tank, but I have 250ml matrix in one of my back chambers which is supposedly  able  to support up to a 25 gallon tank. If you remove a lot of rock from the display I would look into getting matrix, marine pure, etc to offset it. And I would add this to your tank a month or two before removing the rock so it is ready to go. 

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Thank you for your input.  My rock is very porous I think that's why 18lbs takes up so much space.  When I look at other people's tank pictures I don't see nearly as much rock as I have.  So even if I take out half I will still have a lot of rock.  I think I'm going to take out a little this week, then a little next week.  I plan on setting up the new tank in 2 weeks so it will go right in, and I can clean and transfer the rest of the rocks with coral on them.

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Put some biomedia in your back chambers and you're good to go. People frequently overestimate the amount of rock they need but bacteria will populate according to what's required, not how much real estate is available in the tank.


I have an IM 20 Nuvo with ~3 cups of biomedia in a bag in the back chambers and that's all I need.

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You can remove it but do it in “portions” and over longer span of time -  your biofilter needs prober time adapt.


Personally, I would also add something to replace the rock you are removing; Biomedia for sump is a good example

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Remove the rock a little at a time.


I'm a total opponent of using biomedia bags or anything else like bioweels etc. You want the biological filter *in* the tank...not growing on some mechanical gadget that requires electrical power to function.


Ammonia / nitrite reducing bacteria grow everywhere...even in bare tanks. How do you think those bare bottom feeder fish tanks at the fish store keep a biological filter?


As you remove a little rock at a time other bacteria will quickly ramp up to compensate. I would also remove rock from the top. Bottom layer bacteria are what take so long to regenerate.

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What is “bottom layer” bacteria?  While counter intuitive to me, I have been told that denitrification bacteria multiply quickly compared to nitrification bacteria.

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