Tall liverock structure stability

[fisheater]

My tank is 34" tall with 2 drilled overflows and a drilled feed (from fuge) in the center. The feed/return is easy enough to cover as its only about 5" tall. I want to encapsulate the overflow tubes. I plan on drilling some live rock and sliding over the tubes. I just dont have that much live rock. What other options do I have to build towers? Can I use stacked slate (landscape supply stuff) or other rock? If so what do I have to do to safely put it in my tank? Its a new setup that has not cycled yet. I am concerned about rock falling. The tank is so deep its very hard to reach the bottom.

[Mark Bianco]

Go to a place like Bulk reef supply and get some dryrock its only about 2.00 per pound. Look at the video of how to cure the rock before adding it to the tank. When it comes to rock or sand I may be overly cautious but if it did not come from the sea its not going in my tank.

[GrampaDon]

Im not clear on this overflow you are wanting to cover. Can you post a pic ?
Otherwise BRS is great for dry rock.

[slyjosh]

I used BRS Pukani rock for my 30" tall tank and found it porous enough to build a tall, stable rock structure by placing the ridges of each rock in the holes of the rocks below. It also helps that some of the mid level pieces are resting on the back of the tank.

I went ahead and put it together outside of the tank first to make sure it wouldn't collapse.

[postshawn]

If you are saying you have tubes up the the middle of the tank somewhere for your plumbing and want to slide rocks over that you can certainly do that. I got my 36" tall tank and it originally was plumbed like that. I removed the center bottom mount tubes in favor for a HOB overflow. But I made a structure out of PVC that has a base and then about a 24" tall PVC tube going straight up. I then picked up some live rock at my LFS and found some nice slab pieces. I drilled holes in the rock and just stacked them on the PVC and found a nice capping rock to put on top. It all worked out great and has been there for about 8 months now just fine. I imagine you can use your plumbing line if it's in the middle of the tank to do the same thing and just stack rock on it. Like mentioned if you can't afford live rock then get some dry rock. I waiting an extra couple months to afford enough dry rock needed (I bought about 40lbs at once). I figured I'd spend the time either saving the money or curing the rock so I went with saving the money and then using live rock and everything was ready to go when I added my other live rock and water from my old system. The whole thing has an inch of play if I push it side to side but I didn't glue any of the major structures down. I did this so I can just pull each slab off if wanted for maintenance or something.

In this photo it's all setup and you can't even see the PVC running through the middle of the larger rock structure. There's even a slab of rock under the sand. I didn't realize I had that much sand which went in after the rock. So I just figured oh well and buried it. There's about 5 large slab type pieces and a couple smaller ones capping the top.

http://farm8.staticflickr.com/7327/10859145163_2ca62ab55a_c.jpg

[fisheater]

Sorry I dont have a pic I can post yet. The overflows I am talking about are just that. 1" PVC pipe running up about 33" (water level) to allow the tank to drain back to the sump.
I am planning on stacking dry rock/live rock over the pipes once I have drille the rock. My concern is that the towers will be rather unstable. Possibly falling and taking the overflow pipes down. That would be catastrophic failure. 100gal of salt water on newly refinished hardwood floors.
Can I use anything like hydraulic cement to stabilize the rock? What effec wold cement have on the chemistry? How about some type of underwater epoxy? Like this: http://www.poolsupplyunlimited.com/bestprice/AquaBondUnderwaterConcreteRepairCompound50MLUW5000/7226?gclid=CLGquPSN5boCFVRnOgod8D0AUA

[postshawn]

Sometimes you can find PVC the next size up in diameter that will slip over the smaller one like a sleeve. Maybe you can do that to the overflow pipe to give it a bit of extra strength. There are various methods you can use to stabilize the rock under neither. I used a series of PVC elbows and such to create a base and those connected to the PVC going straight up. You obviously can't do that because it's connected to the bottom of the tank. You can try the light diffusing panels sometimes under the rock and sand and have the rock sit on that. Sometimes is just sits better on that then the bottom of the tank. Or you can try maybe glueing a couple pieces of rock or PVC on the bottom around the outer edge of the first rock to hold it in place. Getting that base piece of rock to sit right will be the key. You can then figure out the leveling of each piece on top after. If you can get good slab rock then it should stack nicely. Even if it's uneven you can knock of sections to make it level ok.

If you are doing dry rock I say give it a shot. You can always rearrange or try something else if it doesn't work for you or you don't feel safe with your structure. Even if there are holes drilled in the rock that won't effect anything if you go another route and will just provide more hiding spots for critters and such. Arranging the rock is one of the most fun things to me. I wish I could just get more tanks just so I can arrange more rock. So have fun with that part of it.

One thing to think about with the structure in the middle is water flow. I have my main powerhead blowing across the bigger space in the front. But I have another small one blowing around the back side of the rock. I really should have another small one on the other side getting a different level behind the rock. There's still quite a bit of swim space behind the rock. My tank is a corner tank so I can see behind the rock which is nice too.