Aquatics Unlimited: Articles: Poor Plant Growth
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Poor Plant Growth

for the week of 12/16/99

Some aquarists just don't seem to have that "green thumb" when it comes to growing underwater plants. The plants they purchase hang in there for a few weeks, maybe growing a bit at first, then begin to wither and fall apart. Here are some things to consider:

Are they really AQUATIC plants? Many pet stores sell terrestrial or bog plants like Sanderiana, Hedge, Red Crinkle, Palm, or Princess Pine. These plants do not receive adequate light or carbon dioxide while underwater for long-term survival. Most are fairly thick-leaved and die slowly, so they may last weeks or even months (which may be better than some hobbyists do with REAL underwater plants), but they are for all practical purposes doomed.

Is the light bright enough? Many common hardy plants (Hygrophila, Amazon Swordplants, Anacharis, Vallissneria, Cryptocoryne) will make do with about one watt of fluorescent light per gallon of tank size. Others (Rotala Macranda, Bacopa, Chain Swords, Sagittaria, most red-colored plants) need at least twice that. The light should be left on for 12 to 14 per day, and no, you can't make up for too dim a light by leaving it on longer.

Is there enough carbon dioxide? Carbon is the basic building element for life as we know it, and aquatic plants get much of their carbon from carbon dioxide gas dissolved in the aquarium water. An aquarium with fish and few plants probably has plenty of CO2, but one with many plants may well run short, resulting in slow plant growth.

Are there enough "fertilizers?" In addition to sunlight and carbon dioxide, all plants require a substantial amount of three elements for good growth: Nitrogen (N), Phosphorus (P) and Potassium (K). In most tanks stocked with fish, there is an abundance of each of these, but in newly set up tanks or tanks with few fish, there may be a shortage. Most commercial aquarium fertilizers do not contain these major elements, assuming you have an adequate fish load. In fact, adding aquarium "fertilizers" may contribute to healthier growth, but probably not faster growth.


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

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