Micro Nutrient Content of Rotala ssp. 'Nanjenshan'
Every so often, everyone runs into a problem. We at AquaFlora ran into a strange problem in yearly 2009, when we noticed a few of our plants were not growing at their normal rates, and their leaves had begun to stunt. Algae began to grow, despite our normal diligence to keeping water in top quality. So we began to rule out different situations, and we eventually discovered that we had been adding too much Manganese to our water conditioner. Manganese is a necessary mineral used by all plants, but in higher concentrations, it is known to be quite toxic to the plants. It becomes even more toxic as pH of soils falls (i.e. becomes more acidic). I have chosen to write about this because this condition may affect others as well.
Under normal circumstances, the manganese we were adding did not show up as extremely toxic; however, when we added fresh water to our tanks directly from our source water, we would see plant death and melting within 24 hours. We eventually clued in that our source water was high in CO2 (extremely high, over 140 ppm as measured on an Oxygard CO2 probe). This influx of low pH water would invariably cause plants to melt and die, if they had been grown in one of our tanks (but not if the plants had been grown in our research tanks, which uses a different fertilizer mix). We ran several rounds of tissue analysis, on both affected and normal looking plants (controls), and discovered a few areas where a mineral might be playing a role in the problems we were seeing. Here are the averaged results from the tissue analysis (we chose to use Rotala ssp. 'Nanjenshan' because it had the largest visual difference between 'healthy' and 'unhealthy', and because it is a fast grower):
These results are reported in micrograms per gram of plant dry weight. As you can see, Mn is very high in the sample plant (the one we saw with problems). However, it look more testing to rule out Zinc and Iron as being the culprit as well.
For those of you who are experiencing issues that cannot be explained by poor CO2 (which, I will grant, almost 95% of all issues I have ever seen, in AquaFlora tanks or other peoples', is CO2-related), consider getting micronutrient analysis by your local analytical lab. We have used several, and testing for micronutrients is usually in the $25-$35 range. If you have further questions about fertilizers, or anything to do with aquarium plants, just send me an email at tim@aquafloranurseries.com.