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Planted Aquarium and Substrate

By: Scott Dahlgren

Planted Aquariums and Substrate



Two concepts are very important when choosing a substrate for the planted aquarium: circulation and ion exchange.

Circulatoin


Circulation in the substrate can be totally passive, meaning that nothing is done to move water across the plants' roots. A popular option is to heat the bottom of the aquarium in an effort to move water from the bottom of the tank to the top. The third option is to actually plumb water to below the substrate and force circulation, known as undergravel filters.

Without any circulation in the substrate, an extremely low reduction-oxidation potential develops. Oxygen is readily depleted, and there is no way of replacing the oxygen except diffusion. Life in the substrate starts relying on chemical reactions very foreign to the ones above the substrate. If the substrate is too fine, then the products of these chemical reactions may buildup inside the substrate and burst to the surface all at once. In open waters, gases belch through the mud constantly, but the reduction-oxidation potential is safe because of such large water volume and surface area. If this happens in an aquarium, then the reduction-oxidation potential of the aquarium water will drop suddenly. The solution is to simply use coarse gravel, or to rely on technology to circulate the water.

Heating the bottom of the aquarium circulates water through the roots and also hides the heater from plain view. Giving your plants hot feet is thought to improve their health by many hobbyists; however, there is no reason other than speculation to believe so. Heating cables are often very expensive, especially compared to other styles.

Traditionally, the undergravel filter bubbled air up a tube connected to an empty grated box below the substrate. As the air rises, water rises with it. This water then leaves the tube, and water is drawn in from the grated box to replace that water. This filtration method was attractive because is was so inexpensive. Any debris in the water column eventually ended up on the bottom, which could be siphoned out of the aquarium. To achieve better turnover, use a powerhead to move water up the tube.

For the planted aquarium, the reverse flow under gravel filter (RUGF) may be the single most overlooked option. The real advantage to a RUGF is that water can be plumbed from the surface and bulk to under the gravel with ease. Once plants take hold, then debris from the aquarium becomes fertilizers for the plants. Combined with a canister filter, you have the best filter setup for the planted aquarium. There is no maintenance, no expensive gravels, and nearly upkeep costs. The water stays perfectly still while still being turned over every 2 hours or so. The reduction-oxidation potential in the substrate still drops below that in the water, but the difference is nearly zero. If you use a setup like this, then dosing with iron fertilizers is a must, as plants' roots won't be as efficient at iron uptake. The biggest downfall is that manufacturers who offer a RUGF for planted aquariums charge big bucks, and making your own can be challenging and unattractive.

Ion exchange


A plant's health relies on the substrate to exchange cations with both its roots and the water. So, a setup with no circulation with the bulk of the water must have an extremely high cation exchange capability. Also, without circulation in the roots, organic substrates rich in nutrients can be used, or actual plant soils and fertilizers can be placed in the substrate. Just make sure that the substrate is never disturbed and has plenty of larger rocks throughout.

With the hot feet option, substrates are pretty much the same as without any circulation. However, if you use nutrient rich substrates with a heating cable, then expect nutrients to find their way into the water column. Make sure you have some plants that take their nutrients from the water column to avoid algae blooms.

Undergravel filters require larger substrate, and avoid using too much organic material. There are a variety of attractive inert gravels out there made for the planted aquarium. Fluorite is an excellent option, and I like to mix about a cup of peat per 5 gallons of fluorite with an undergravel filter. But, I've also had great success with regular aquarium gravel, nothing else.

Best Bet


Plumb an overflow to a canister filter, to a heater, to a carbon dioxide reactor, to an undergravel filter. With this setup, the water chemistry throughout the entire setup is almost identical. The tank circulates top to bottom, evenly. Adding small amount of fertilizers frequently will be required for good growth, and this can be automated easily.

Substrate choice is largely aesthetics in this setup, so expensive gravels may look better and be the right choice, or that mixture of lavender and hot pink gravel may be just. Although substrates with high cation exchange capabilities will outperform regular gravel, this can be offset by increasing volumetric flow under the gravel.

Atlanta Aquascapes

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