Aquatics Unlimited: Articles: Fertilizing Plants
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"Fertilizing" Plants

for the week of 2/25/99

Like so many other aquarium issues, whether or not to fertilize aquarium plants depends on what sort of tank is being kept.

An aquarium with many fish, few or slow-growing plants, and standard lighting (less than 1 watt per gallon) may require no more plant nutrients than what are available in the form of fish waste. Since plant growth is very limited, any additional plant nutrients will likely result in an algae outbreak.

Tiger BarbAn aquarium with a moderate to heavy fish load, faster growing plants, and better lighting (one to two watts per gallon) may need partial treatment. The fish waste may well supply enough of the major elements (nitrogen, phosphorous and potassium), but rapidly growing plants may begin to run out of trace elements, especially iron. Discoloration or transparency of new leaves indicate the lack of one or more important trace elements. Such tanks should be regularly treated with an aquatic plant supplement that contains iron, but little or no nitrate or phosphate. Overdoing the nitrate or phosphate may again lead to algae blooms.

Planted TankAn aquarium with low to moderate fish load, many rapidly growing plants and excellent lighting (three to five watts per gallon) may need a full-blown "fertilizer" - especially if carbon dioxide is being added to the tank. Under these optimal conditions, the plants may use up nitrogenous waste faster than the fish are excreting it. In such "nitrogen-limited" tanks, plant growth slows and ammonia, nitrite and nitrate readings are all near zero. And sure enough, algae once again takes over. These tanks should receive a supplement that includes both the trace elements and nitrogen and potassium (phosphorous is rarely in short supply).

"Tip of the week" appeared regularly in 1999 and 2000.

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