Measuring live rock?


New member
Okay, I decided to thread this question. Why is it suggested to have 1-2 lbs of LR per gallon?

The reason I ask is:

180 lbs of LR, depending on kind, could seriously cut down on space in my or anyone's aquarium. The lighter rocks, like Fiji, would nearly fill up my 90 gallon tank. Heavier ones like Pacific shelf or Vanuatu, would barely fill 1/3 of the tank.

What really confuses me is the the more porous, lighter rocks, will have much, much more surface area for biological growth than would the heavier, less porous rocks since they would have less surface area. So I have to ask why, would it not be suggests to double the amount of the less porous rocks to make up that surface area? OR lessen the quantity of the lighter rocks? Maybe suggest a volume and not a weight? Harder to quantify I know.

I know folks are placing quantities of LR in sumps to leave the DT more open. Still, I have 55 lbs in my 90 gallon tank and am wondering where the rest is going to go!


Active member
Thats a really good question/observation and im curious to know the answer. I would also add the fact that your bio-load would also greatly affect your need for more/less rock because your need for filtration would be different.


New member
You answered your own question, you should aquascape your tank to your liking, there is no magic formula. You do want to allow for enough rock to provide ample area for bacteria colonization, obviously the more porous the rock, the less it will weigh & vice versa. I would use around 150-200lbs of Live Rock in a 180g, but that's my preference, I like the peak, valley, peak type scape across the whole aquarium, looks more like a natural reef formation to me.

Ron Reefman

New member
The advise is 1-2 lbs per gallon. 1 lbs/g if it's light rock and 2lbs/g if it's heavy rock (I just made that up... but it makes some sense). It's just a suggestion. The heavier your bioload is going to be, the more LR you would like to have. More LR, more places for ammonia and nitrite eatting bacteria to live. More fish, more detritus, more ammonia.


New member
every tanks is different, iv got a 240g with 90p bali rock which is very light and porous and 100p sand but only 5 fish, i have a zero reading across the board with feeding allot.