A couple aquascaping questions.

[bob965]

In tanks with really high mounds and slopes and formations, is there anything placed underneath to help achieve the height, or is it just simply a uniform pile of the substrate? If it's all substrate, is there any danger of toxic gasses accumulating underneath?

What can be used as a divider in the substrate to keep a ground covering plant confined to a specific area?

 

[FLESHY]

It sounds like you are talking about iwagumi. To start it out, the creator usually puts a piece of cardboard up where he wants the division. Then he piles the substrates (there are usually different things in layers) and then when he has the desierd effect, he carefully removes the cardboard.

Then one uses rocks and driftwood to help hold the form for a long time. Other than that its just substrate pilling.

To keep plants out of a certain area, most people use "decorative sand". This will not have the nutriets of the rest of the substrate and plants will struggle growing into it, or at least will grow in slowly, making it easier for the aquarist to maintain.

Sorry I dont know about the substrate oxygenation question...

 

[jcardona1]

to achieve higher height, many people use bricks or rocks under the substrate...

 

[Pyramid_Party]

Also MTS (Malaysia Trumpet snails) will help with gas issues in the substrate.