GRAVEL/SUBSTRATE vs BARE BOTTOM
Everyone needs to keep in mind that an argument is a truth-seeking process in which both sides respect the other's opinion. I believe what this situation boils down to is a matter of preference. Here is what I believe, and it is only my opinion:
1. Aquariums with natural substrate (No pink or blue gravel) look more aesthetically pleasing than aquariums with bare bottoms, but that is only my opinion and this comes down to ones partiality.
2. The extra 2" of water depth is insignificant in most cases, fish will stay in the strata they are comfortable in and I highly doubt they miss the room that is sacrificed by having substrate. If that volume of water is critical, please upgrade.
3. The extra water volume that is sacrificed in favor of substrate DOES mean there is less water in the system for hazardous chemicals i.e. Nitrate to diffuse in. The inverse to this argument, that gravel increases the BB and Bio-Filtration is also highly valid. Unfortunately neither is enough to sway the debate:
If the aquarist is doing regular water changes, the extra water in the system doesn't matter.
If the aquarist has ample bio-filtration to handle the bio-load of the aquarium, the surface area added by the gravel doesn't matter
4. The aquarium is easier to keep clean by having a bare bottom, and is easier to CONTROL water quality. This doesn't mean a substrated tank will have lower quality of water. Clean/Chemistry/Quality are all separate entities. It may be easier in a bare bottom but easy does not = better. Once you throw in plants and sumps this item of the argument will have too many variables and will come down to an individual issue. I personally enjoy the challenge of maintaining pristine water quality while having fish, substrate, and plants.
5. The weight issue boils down to simple physics. If your tank and stand are built properly on a sturdy foundation the difference in density (Density=Mass/Volume) between water and gravel will not cause catastrophic failure. Gravel is typically a little under twice as dense as water, but once submerged it loses much of its weight (Mass with downward force [gravity] included). If you are worried about the weight, calculate the numbers beforehand. This is a good site to see the density of different materials -http://www.simetric.co.uk/si_materials.htm
6. It has been suggested in many aquatic journals and forums that the color of the substrate of an aquarium can have an affect on the coloration of a fish. Parachromis Managuense keepers will argue that the darker the substrate, the more vibrant the coloration. Symphysodon aequifasciata keepers will often discount this notion.
In conclusion it is my personal belief that unless your tank’s purpose is a quarantine or possibly a breeding tank, the aesthetic benefits and the ability to better house plants tilts the argument in the favor of gravel, But that’s my opinion