I've been meaning to do a write up on how I created elevation changes and supported large objects in my dirt'd tank.
I started with Miracle Grow Organic. I used a kitchen strainer to filter out all the wood, and large junk/filter in the potting mix. It took about an hour to strain out a gallon of workable soil. I baked the potting soil, at 350 degrees for about an hour before straining it. The dryer soil was easier to work with. I used nearly 4 gallons 'filtered' soil and had over twice that amount of waste product.
I poured the dry MGO into the tank, shaped, filled and than carved out areas that would be supporting my rock features. (I also curved out, areas on the right tank, to reduce the soil needs of the hill, using the extra soil elsewhere in the tank - not shown). I keep spraying the soil with water from a handheld spray bottle. The soil is easier to form and shape when it is slightly wet.
I filled the bottom of the holes in the MGO with fill sand about 1/4 inch. This is optional. The sand will help hold the gravel fill in place. Spray the stand with a little water.
Next I filled the hole, with cheap aquarium gravel. I used gravel, from a smaller
(10 gal) tank I shut down a few weeks earlier. Once, the fill gravel was in place, I placed the rock features. Than filled the feature with more gravel. Use a hand sprayer to keep the gravel wet. Note: the gravel is not level with the feature. Leave room for plant gravel (in the case Fruval). The rock feature forms a "bowl"
I thank capped off the rock feature off with Fruval planting substrate.
I used the same method, to create the hill on the right side of the tank, as well as embed, the other rock feature.
This area will settle a little, so I'll cover in, as well as the MGO with Eco-Complete. There will be a inch or more of eco-complete substrate covering the MGO.
Before adding the Eco-complete, I used the hand sprayer to saturate the soil. This took a very long time. I allowed the soil to soak over night, before scooping on eco-complete one cup at a time. Take your time doing this. All the effort you put into this will save you from a cloudy thank once you fill it with water. I have noticed there are not any air bubble trapped in the MGO base when I used this method. My other planted tank, has lots of air trapped in the MGO base, as I rushed to fill it with water.
Here's the end result.
and a close up of the close-up cliff (rock feature)
I've only started using a Fennix FugeRay2 and pushing CO2, this week. I'm expecting some real growth shortly.