"Padding" under raised section of a river tank?

[isuchopper]

Hi folks-

I'm in need of a little help here. I'm designing a river tank where one side will have a raised 'stream bed' so that I get faster water flow and the other side will be the full depth of the tank so that the current will be pretty minimal.

The problem is that I need a way raise up that 'stream bed'. I started by using a 4 inch thick section of the pink house insulation foam, but it's so bouyant that I needed to pile on 40 lbs of rock to keep it underwater. Not good since I'd like to avoid having to glue this in place.

So...I'm planning on using egg crate but I think I need something to pad the bottom of the egg crate so that I don't trap a small pebble and bust the bottom of the tank. My concern stems from my plan to have a fair bit of rocks on top of this raised section of the stream bed. I could make my own sheet of silcone to use as a padding layer from a large tube of aquarium sealant, but that sounds a bit tedious.

Any advice on materials for padding or whether I need it at all?

Thanks.

 

[Brass sliver]

I have 60 lbs of gravel in my tank and another 85 lbs of limestone and my tank is fine. I did however put egg crate directly on the glass, put my limestone on it and then added the gravel. I keep cichlids so I did'nt want them to dig under the rock pile and have it tumble down risking killing a fish or busting my tank. Putting egg crate distribute the weight on a larger area so that there are no pressure points. A pressure point is really what is gonna bust a tank.Make sure that there is nothing in between the crate and the glass and it should be ok. what size tank, how thick is the glass. If the bottom is well supported, glass is stronger than one might think.

 

[isuchopper]

Brass-

Thanks for the reply. Unfortunately, this is just a standard 20 long. I realize I'm being paranoid about breaking the glass, but I figured that I ought to look into ways to minimize the risk. I think have to put a solid sheet of plexiglass down anyway (for my support design), so I think that I'm going to just apply a thin covering of silicone to it so that I can sleep better. Thanks for the advice.

Mike

 

[RTR]

I use egg crate as well for weight distribution for large rocks or sizeable rock walls (mbuna tanks, etc.). The egg crate alone will be more evenly supported without a silicone layer under it. IMHO that will cause you more issues than it will solve.

Any rock structure should start at the eggcrate. Having eggcrate topped with gravel and rockwork atop the gravel is asking for problems. Build up your rocks and then fill in the gravel where needed.