Q. My first planted aquarium is about 2 months old. Lately, I’ve been having trouble with my Echinodorus barthii and Radican marble queen sword (Echinodorus cordifolius). Some of the leaves have been turning yellow, then falling apart; others have just been coming off (the base of the stem looks brown but the rest of the leaf looks fine). Most of my other plants are doing well, the swords seem to be the ones with the big problem.
I’ve got a 50-gallon aquarium. The pH is about 7.2. Temperature is 78 Fahrenheit. Nitrate is 10 ppm, GH 150 ppm, KH 40 ppm and phosphate 1 ppm. I don’t have an iron test kit yet. I have three 20-watt fluorescent bulbs rated at 70 lumens. I have a yeast-activated carbon dioxide injection system, and most of the bubbles are absorbed as they pass through the reactor. I just started adding a fertilizer in hopes that might help. I’ve also been thinking about getting more lights, even though the bulbs have high lumen ratings.
Any suggestions on how to save my swords?
Thomas Simpson Hockessin
A. It sounds like the rosette, the central base of the aquatic plant, is rotting. The plant might have started rotting before or after you got it. If the new leaves are clean all the way to the base and show no signs of deterioration, the plant might recuperate. Your lighting is at the very low end of what the swords might easily tolerate. I would give them at least 1.5 watts per gallon or preferably closer to 2 WPG to maintain the red color in the E. x barthii and growth in the E. cordifolius. That is assuming the reflector is made of mirrorlike polished metal rather than white plastic. If the reflector is plastic, I would aim for about 2 to 2.5 WPG.
The nitrate and phosphate levels are good: one-half to 1 ppm of phosphate and 5 to 10 ppm of nitrate are good levels of those nutrients. However, overfeeding of the fish, especially if you are adding phosphates or nitrates as fertilizer, could lead to excesses of those compounds. If you are adding fertilizers, be sure to keep up on your water changes (50-percent weekly) to ensure that you do not accumulate excess nutrients. Alternatively, you can measure phosphates and nitrates, and do water changes less often but always whenever the phosphate or nitrate levels get too high. If you maintain carbon dioxide levels at about 20 to 30 ppm and have lighting close to 2 wpg, you will probably need to add phosphates and nitrates to maintain the levels of those nutrients. I definitely would add a good trace mix to ensure adequate amounts of micronutrients, including iron. The amount of iron needed will be supplied by the trace mix.
It is interesting that your general hardness (GH or calcium/magnesium content) is so high (150 ppm or about 8.4 degrees), while the carbonate content (KH or alkalinity) is very low (40 ppm or about 2 degrees). At that carbonate level and a pH of 7.2, the carbon dioxide level is only about 4 ppm or roughly what it would be if no carbon dioxide were added. This could be an error in the KH or pH readings, but even assuming a wide margin of error, it still looks like the carbon dioxide level is very low. The swords would benefit greatly from a carbon dioxide level of about 20 to 30 ppm. I would first raise the carbon dioxide levels, then think about adding at least one more bulb. You might need a second carbon dioxide fermentation bottle to increase the carbon dioxide input, or you might need to reduce the rate at which the water sheds carbon dioxide by lessening water surface turbulence. With the low KH you have, there is not much buffering capacity. On the other hand, the high GH indicates that you probably have plenty of calcium. Therefore, I would raise the KH by adding baking soda with water changes. One teaspoon of baking soda (sodium bicarbonate or NaHCO3) per 10 gallons of water will increase KH by about 4 degrees (71 ppm) and will not increase general hardness. I would raise the KH to about 4 or 5 degrees (70 to 90 ppm), then add carbon dioxide to reach a pH of about 6.6 to 6.8.
If the base of a sword plant is buried in the substrate, the base can rot, especially with newly planted specimens. Plant the specimens so that the very base of the petioles is just at or slightly above the substrate. When you get a sword plant from a store, it has probably been grown at the nursery with the leaves out of the water. This is a faster way to grow sword, but those leaves will eventually be shed by the plant as it grows submerged leaves, which will have much shorter petioles and longer leaves. When you get the plant, cut away about a third of the length of the roots, and peel away about a third of the outer leaves and any leaves that are badly damaged or brown. You can leave one or two long roots on the plant to help hold it in the substrate until new roots take hold. Also, any brown roots are dead, and should be carefully snipped or pulled off. If the plant comes with the roots in rock wool, remove as much of the rock wool as you can, using a pin and/or your fingertips to comb it away carefully without tearing the roots. In my experience, the rock wool tends to promote root rot, especially if any dead roots are in the rock wool. Renowned aquatic plant expert Christel Kasselmann also recommends removing the rock wool. However, I believe her primary concern is that the rock wool fibers, if they get into the water column, can be harmful to the fish gills.
Watts per gallon is not a highly accurate way to assess how much light plants receive, but it is an adequate and handy method. Lumens are actually not as useful. Lumens measure the light to which human vision is sensitive, and we are mostly sensitive to the green band of the spectrum. Thus, a large part of a lumen measurement tends to be in the green range of the light spectrum, which is the range that plants tend to reflect rather than use for photosynthesis. If you use good broad-spectrum (tri-phosphor) fluorescent bulbs, then WPG is useful way to gauge light levels.