Water Weight: Dry Rock vs. Live Rock

Ya... you had it right, you are just using the wrong terminology when it comes to displacement. Displacement is about two things can't occupy the same space. So displacement in a tank is about how much space the actual rock occupies. So wet or dry has nothing to do with that.


Lace rock is volcanic rock. It does not look like lava rock used in barbecues say... but it is flat and obviously looks like it was molten at some point. Problem is though it is pretty solid and not very porous. You want porosity and holes for creatures and bacteria to inhabit.

Use lace rock as decorative pieces. good shapes for bridges or some cool structure, but don't count it like reef rock. It does not come close to the surface area that reef rock has.

It's the surface are you are after, not the lbs.

 

Here is the rock in my tank(dry rock).


This is the 8 lbs(I think) of lace rock I bought on Tuesday.

 

Yep, that's lace rock and some cool looking pieces too.

 

No, wet rock displaces more water in the tank.

The reason is that dry rock lets water flow into its pores while wet rock is already full - thus causing more displacement and less absorption.

This assume of course the densities of the dry and wet are the same.


Additionally, I've done some experiments on this using FL rock as well as TX holey rock. What I have found is that wet rock is heavier than dry rock (I let wet rock dry out for 3 weeks). Of course right

BUT, it's minuscule difference IMO. Very small % change in weight after dried out (technically, I nuked it and then dried it out, so some of the weight loss is matter, not even water). Majority of the water flows out of rock when removed from the water. It is heavier, water is retained, but it's not so big a difference to be concerned. People make a much bigger deal out of this than I feel is warranted.

The example I remember off the top of my head is a piece of 4lb and 3 or 4 oz FL rock. After nuking and drying out for several weeks, that same piece weighed like 3lbs and 14oz. It had only lost maybe half a pound in weight. That *is* significant (and would add up for 70+ pounds), but I feel a lot less than people assume. And since only a small portion of your rock is live rock ... it doesn't really add up (since you buy mostly dry anyway).

Based on the difference in weight, I also continue to support the idea that TX Holey rock is exceptionally good at anaerobic bacteria cultivation in your tank (thus being really good at helping keep nitrates down). Because it is dense, but not so dense that water/anaerobic bacteria can't live in there. Makes sense to me that traditional LR will have more aerobic bacteria and TX Holey will have more anaerobic. Some of you know I have maintained 0 nitrates for several years now. I give that rock partial credit.

You have a point on the price scam, making you pay for water, but you're also paying for them keeping it in good wet conditions (hopefully). It's cheaper to sale dry rock in a tub than it is to maintain rock in an aquarium... so I don't completely agree that buying water weight is a scam.

 

Thank you for sharing your experiences. So would you say that the dry rock I have is okay to buy for when I add more?

 

I know you love your Holy Rock Peredhil, but you have a long way to go proving it.

Holy rock has quite a smooth surface compared to most other rock. Very tight, not very porous. The thing is aerobic bacteria live where oxygen is so that is on the surface. Anaerobic bacteria live in low oxygen which means deeper in the rock. So it would seem backwards to what you believe the benefits of Holy rock are.

 

No, you do not want to fill up your tank with dense rock. You want reef rock that has a huge amount of surface area and habitat space for all kinds of critters.

Lot's of folks use lace rock... however, many are critical of it that you can't guarantee that it does not contain heavy metals. Also other will contend it has silica in it. I had maybe 10 lbs worth in my 90g.

But besides that, compared to reef rock it is very solid. You can still buy dry rock. The funny thing is lace and holy rock is so dense that when you buy it by the pound, you are paying much more than you would if you bought dry reef rock. Ya I was only paying $2/lbs but a little flat piece I wanted for a shelf cost $20.

You can easily find live rock for $2/lbs on craigs list. Hook up with a local reef club. Most members have plenty of dry reef rock sitting around that they will sell for $2/lbs. And that for dry. You don't have to go to a fish store. Live rock is cheap to come by if you have patience.

 

I've already proved it. With the weight test. If it were lead, like you are kind of suggesting (not literally of course) the dry and wet weights would be identical. Since dry weighs less, it is clearly permeable.

Since it *is* permeable and since the permeations (is that even a word lol) are tighter as you point out it only stands to reason less O is available encouraging anaerobic over aerobic as you again point out.

The more openly porous your rock is, even the deep pores are going to allow more O bc they are less tight. I believe your view is backwards to be honest.

 

I do agree with all these points.

I would only recommend dense rock (and specifically the Holy Rock) as a subset of the rock you have. The majority should be much more porous.

 

I'd also like to say, short of being able to measure available bacteria, I don't see a way to directly prove this one way or the other.

I can only indirectly point to it and give my experience (and my lack of nitrates) as supportive evidence. But I do concede it's not direct proof.