Rocks in tank question - Tropical Fish Keeping - Aquarium fish care and resources
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post #1 of 5 Old 11-01-2011, 12:50 PM Thread Starter
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Rocks in tank question

So I am already planning my next aquarium, probably will start buying stuff for it after Christmas (still working on my 29 gallon, man these things are addictive!). I am going to be doing either a 55 or 75 gallon African Cichlid tank. I have been reading up on them, and have seen that the Malawi Mbuna Cichlids like lots of rocks and caves, etc. I live right next to a river so have been collecting fairly decent sized rocks and plan on cleaning them to put in the tank. My question is, it will probably be quite a bit of weight on the bottom on the tank, and I'm worried about it putting too much pressure on the glass. Obviously people use rocks in their tanks, but is there anything special I need to do? How much weight will be ok in the tank? Just nervous of a 55/75 gallon tank breaking and leaking all over the living room due to too much weight from rocks, would not make my husband happy!!
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post #2 of 5 Old 11-01-2011, 02:13 PM
There are a few things to consider with this query.

A. Will you also use a gravel/sand substrate?
B. If so, will you just use a couple-few rocks in the tank?
If not, see below.
If so, you should be fine.
C. If not, will you just cover the bottom of the tank with a layer of rocks?
If just a layer or so, you should be fine.
If several inches, see below.

Below: If you're using a lot of substrate and rocks or just several inches of rocks so that the glass bottom is absolutely 100% covered, you might consider creating a brace to go across the middle of the tank or two to go across the 1/3 and 2/3 marks in the tank.

Remember tanks were created to hold enough weight for substrate; most likely, you will be fine. I wouldn't use more than 40 or 50 pounds of river rock, though.
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post #3 of 5 Old 11-01-2011, 02:34 PM Thread Starter
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I will be using a sand substrate, probably 1.5-2 inches thick, so that will be 150lbs of sand or so. I know that the tanks I've seen for some Cichlids have rocks piled halfway up the tank, and it just looks like it would be so heavy for the tank bottom! I carried up about 100lbs of rocks from the river today (arms hurt, thank goodness for P90X!!) so I will have to figure out which ones work the best for making a rock wall or two without getting too heavy. Thanks for your help!!
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post #4 of 5 Old 11-01-2011, 02:41 PM
I don't know if you have a basement/crawl space, but make sure your floor can handle the perpetual weight of the tank without bowing. You should be just fine, though!
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post #5 of 5 Old 11-01-2011, 03:15 PM
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Some people buy a plastic grid -like product in lighting section of a home improvement store. Its called "egg crate" and it is meant to be a diffuser on those four foot fluorescent fixtures. But you can buy it, cut it to the size of your interior tank bottom, and place it there first before adding any substrate or rocks. The theory is that this will help dissipate the weight. I would also recomment adding rocks before substrate, so that the rocks sit directly on the tank bottom. This is important because if a creature digs at the base of a rock that is sitting on top of the substrate, it could collapse the entire structure. Also, there are rocks sold at fish store that are more porous, and therefore lighter weight, than collected rocks. The are usually calcerous, but fine for a hard water set up like this. Also, it is wise for the fish's safety and the integrity of the tank to secure the rocks to each other and the tank wall if you build higher than one "story". A moldable compound is sold for this purpose, perhaps someone with more experience with this product can elaborate. You could also silicone it together, as long as you were cool with the semi-permanence of this option.

As an aside, but sure to be careful about your rock selection (i.e. metallic veins, etc.)

I have no experience with mbuna, but I did once have a cave setup. Good luck, the build is great fun!

"My dither fish need dither fish!"
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