Continued from page 2
- Case Study 1
- Case Study 2
- Appendix A - Fertilizer Recipe
- Comments on this Paper
- Later comments on this Paper
Case Study #2
Initial conditions as of May, 1994: 160 L tank, 12 cm of 3 mm gravel with 1.7 kg of Terralit in the bottom 3 cm. Canister filter with carbon, 80W of cool white fluorescent light, CO2 fertilization, very small fish load (6 flame tetras). Water hardness approximately 120 ppm CaCO3 equivalent, pH ~7.0, temperature 25C, 25% change every few days.
Plant growth was slow, and brown algae that appeared to be a form of cyanobacteria (rapid growth in sheets, easy to remove) grew on the plants and substrate. Attempts to control the algae by frequent water changes and mechanical removal were ineffective. All water changes were accompanied by disturbance of the top 1 cm of the substrate.
Change: A potassium/iron fertilizer was added (0.9 ppm K, and 0.06 ppm FeIII) to the replacement water at water changes. The fish load was increased to 23 flame tetras (6 adult, 17 juvenile) and six otocinclus. The cool white lights were replaced with inexpensive plant tubes.
Effect: No change noted.
Change: K/Fe addition was stopped, and plant tablets (10-14-8) were inserted into the substrate in small pieces near plant roots. A total of 35g of tablets was added over a period of few weeks.
Effect: Some improvement in plant growth was observed. Unicellular green algae proliferated, reducing the visibility in the water to as low as 25cm. Frequent water changes had little effect on the algae.
Change: Fritz Super Clarifier (active ingredient(s) unknown) was added as directed to the tank water.
Effect: The unicellular algae became trapped by the filter. Because a recurrence was expected if the aquarium parameters were not altered, another change was made immediately:
Change: Addition of trace elements (homebrew formulation of Fe, Mn, Cu, Zn, B, Mo, and EDTA) with potassium sulphate at water changes. The dosage was computed to give 0.1ppm iron and about 1ppm potassium in the replacement water. Carbon was removed from the filter.
Effect: Plant growth improved, but blue-green cyanobacteria appeared and began to spread. Nitrates were found to be unmeasurable.
Change: Addition of potassium nitrate began in 1-2ppm NO3- doses, initially once every 5 days, increasing to daily once the author [Sears] became convinced of its lack of toxicity at these concentrations. Potassium sulphate, previously added to replacement water, was now dosed with the potassium nitrate at about 1-2ppm K. A commercial trace element mix (composition given in Appendix A) replaced the homebrew formulation. Magnesium sulphate addition was begun shortly after at a concentration of about 0.25ppm Mg.
Effect: Significantly better plant growth, but patches of cyanobacteria continued to grow on the plants and substrate. Green thread algae appeared on the brightly lit parts of plants. It was found that nitrate introduced to the water in 1-2 ppm doses was not detectable one or two days later.
Change: More plants were added. In the process, several old plants were uprooted, exposing the buried fertilizer tablets to the water.
Effect: Increase in green algae and blue-green cyanobacteria.
Change: Disturbance of the gravel at water changes stopped. Specifically, gravel vacuuming was discontinued, and replacement water was poured into the tank gently. Since the substrate evidently still contained considerable phosphate in the form of undissolved fertilizer tablets, it was thought best to disturb it as little as possible.
Effect: Algae of all types declined rapidly. It no longer appeared on the leaves of fast-growing plants, and apparently died and fell off the older leaves of slower-growing plants.
Change: Reduction of hardness of water to 60 ppm CaCO3 equivalent. This resulted in a drop of pH to approximately 6.7 (which was the reason for the change), and a temporary jump in the iron concentration in the tank, from less than 0.2 ppm to 2 ppm.
Effect: All Cryptocoryne sp. in the aquarium lost some leaves. Algae continued to decline.
Current status: All of the plants in the tank are growing well, including the Cryptocorynes that lost their leaves. Stem plants require weekly trimming, and floating plants need thinning every few days. The only algae in evidence are some small patches of cyanobacteria on the substrate and a little green algae on brightly lit parts of the Vallisneria gigantea, the Cryptocoryne balansae and the Bacopa caroliniana. Disturbance of the substrate (for replanting of cuttings) has led to minor algae outbreaks (green algae if the nitrate concentration is at least few ppm, cyanobacteria otherwise). Small amounts of (apparently dying) material are still in evidence on some of the oldest Anubias barteri var. nana leaves. The water change frequency has been reduced to 25% every two weeks.
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