? about putting rocks in my tank

kalija · Post by **kalija** » 15 Jul 2005, 03:30

I was going to build some rock caves in my tank, not a huge rock pile, just some ledges and caves. I have been told/read that I should put a sheet of plastic or styrofoam under the rocks to prevent a pressure crack. The thing is, I have a mixture of sand and fine gravel in the tank already, and even if I remove it first, isn't it going to get under the sheet of plastic eventually? I would think this would cause more chance of problems. Plus if I used styrofoam I would be worried about plecos eventually chewing on it. So I am wondering if it is really necessary, or can't I just put the rocks on the tank bottom in the sand? Its a 125 gallon, so I definitely don't want a leak! Thanks!

Post by **Birger** » 15 Jul 2005, 05:38

what you can also use is the plastic egg crate sheets used for flourescent lighting.
It is only a few dollars a sheet and is available at any decent hardware store.
Can be easily fitted as well, I just cut it with side cutters(wire cutters)

It is well worth the trouble!

Birger

MatsP · Post by **MatsP** » 15 Jul 2005, 10:40

Styrofoam is easily available in sheets at the local DIY/Hardware/building (Home Depot or similar in the US, B&Q/Homebase in the UK for instace) shop. You don't need a thick piece, just a quarter inch (6-8mm) or so, but thicker is fine too, as long as it's not several inches (more than 50 mm). Too thick is mostly a problem with floatation, that it will require a lot of rock to weigh down the foam, and it will cause a problem covering it up with gravel.

Any other firm foam, such as firm polyurethane foam would also work fine.

The point is that you don't want any sharp edges/bumps of your stones to be in direct contact with the glass, and you shouldn't put the stones on top of gravel if you have (or will get) some fish that may dig, as they can undermine the rocks and make them fall over. In the relatively good scenario that kills some fish, in the worst you've got 125 gallons of water on your floor as well as dead fish...

I don't think plecos would chew the styrofoam, but even if they do, it shouldn't cause any big problem, as it's extremely unlikely that they would get under the rock to cause any problem.

Gravel under the foam shouldn't be a problem, as the plastic should be soft enough to "soak up" the gravel pieces that end up under it, and it's unlikely (that word again) to end up under the actual big stones.

What you don't want is a pressure point and ensuing cracked glass from the stones.

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Mats

bronzefry · Post by **bronzefry** » 15 Jul 2005, 15:41

I've never heard this one. You learn something new every day. I just put the rocks in the tank. Doesn't styrofoam float?

Post by **corybreed** » 15 Jul 2005, 16:54

I don't like the idea of using styrofoam under the gravel. I beleive that using styrofoam of any thickness would create dead space and encourage anaerobic activity. Lay the rocks on the bottom of the tank glass first then add the gravel. Make sure the tank is level. It is much more likely for a large tank to leak because it is not level than from a pressure point created by a rock. If the styrofoam is exposed some Loricarids would graze on it.

Mark

kalija · Post by **kalija** » 15 Jul 2005, 17:08

Thanks for the replys! I had another thought - what if I put a thin layer of aquarium silicone on the bottom of the rocks and let it dry, instead? Wouldn't that absorb the pressure just as well? Thanks.

MatsP · Post by **MatsP** » 15 Jul 2005, 18:11

bronzefry wrote:I've never heard this one. You learn something new every day. I just put the rocks in the tank. Doesn't styrofoam float?

Styrofoam floats itself, but if you put a couple of pounds of stone on it, it'll stay down...

To comment on the other ideas: Just put the stone on the glass will work fine if your tank is designed such that it sits on a firm surface underneath the glass, but if there's a gap, and you have a BIG stone, you'll try to bend glass at the point where the stone touches the glass. If you have a bit area where the stone touches, that would be fine (for instance flat stones like slate), but if it's a small point, you could have a problem.

My initial answer was a "This will always work" answer, whilst the "Put rocks on the glass" is a "Will work if you're not stupid or unlucky". I always try to give advice based on "will work", rather than "requires person to have common sense and/or luck". I'm not saying the Original poster doesn't have common sense (or luck for that matter), but I'd rather rely on my sense of "This will guaranteed work".

I've had stones directly on the glass in several tanks, no leaks [other than a stupid me not connecting a hose back and emptying much water through the external filter...

]. But that's not necessarily what I'd tell someone else to do... My tank: my chances. Someone elses tank, I don't take chances... If that makes sense...

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Mats

DeepFriedIctalurus · Post by **DeepFriedIctalurus** » 16 Jul 2005, 05:48

What about cutting a large commercial-style rubber floormat to size? It could be sold by the foot too, for all I know. You might even be able to slip this under the substrate if you move it all to one end & then the other. I could see thinner foams getting compressed in some spots & still allowing a focused pressure point through, then the diffuser panels already mentioned for fluorescent lighting can crack/break themselves.

Only possible downside I can think of is the possibility of chemicals leaching out of it. Contacting the manufacturer of whatever's available to you could confirm that..

bronzefry · Post by **bronzefry** » 16 Jul 2005, 14:38

A lot of those floor mats are chemically treated. The days of pure latex or rubber are gone. I haven't had any problems with smaller rocks. About once every 8 weeks or so, I like to take them out for a scrubbing. That's just me. To each his/her own.