Approaches To Supply Nutrients For Aquatic Plant Care

Previous articles have addressed various nutrients and their roles in aquatic plant] uptake, metabolism, enzymatic adaptations, physiology and cycling. This month’s methods for supplying nutrients to submersed aquarium plants: the substrate and the water column. These two locations have been hotly debated over the last 20 years and very intensely since the introduction of PMDD(Poor Man’s dosing Drops, or some referred to them as Poor Man’s Dupla Drops) back around 1995-1996.

For the best results with aquarium plant substrate, I highly suggest that everyone reading this also read the Sears and Conlin paper. Water column: Paul Sears and Kevin Conlin among many others from the APC mailing list helped to developed a low cost simple plant nutrient formulation using KNO3, MgSO4, K2SO4 and the CMS+Boron trace mix. This approach was based upon Liebig’s law of minimums and the prevailing limnology of northern lakes and papers from such researchers as Phillips et al 1978.

The main concept was to provide enough PO4 for plant , but not enough for algae to thrive. I had high PO4 in my tap water while dosing KNO3, K2SO4 and good traces, along with high CO2. Most hobbyists at the time (early to mid 1990’s) had 2-3 mm plain sand substrates, with laterite mixed into the lower 1/3 of the layer. Essentially this method was relying mostly on the water column for plant nutrition. This provides guideance on Aquarium Plant Food. Several Dutch and German hobbyists had been adding soil and loam and getting good results as well and not adding KNO3 and K2SO4, but generally used Tropica Master Grow which has some Mg2+ and K+ added. Scientific support based on natural systems had significant support for this culture method (Barko and Smart, 1985, Phillips et al, 1978).

This enabled both approaches to work well but neither has significant growth over long time frames without re-enrichment of the soil, often experiencing unexplained lulls in plant development and problems with growing particular aquatic plant species. It is also important to note, historical light intensities where much lower than today’s standards in terms of efficiency, color spectrum and reflector use. 1.5 to 2.0 wpg where the normal ranges using T12 fluorescent lighting without reflectors at that time. 15ppm of Carbon Dioxide was the normal suggested CO2 range. Micronutrients where added based on test kits for Fe. This means that growth was much slower and the aquatic hobbyist had much more room to work with in terms of the sources of nutrients, smaller loading from biological waste still provided enough for the plants to get by fairly well, substrates alone could supply most of the nutrients at the slower growth rate. Then high light power compact fluorescent lighting dropped in price as did metal halide lighting.

There was a strong trend to more light and higher color temperature. This in turn, led to more dependency upon inorganic fertilization approaches, much like farms that require fertilizers to grow their crops year after year rather than a “balanced ecology” concept where food is gathered from wildlife and no fertilizers are utilized to enhance plant growth. When conversations of “balance” are brought up, the focus should be on balancing the natural biological waste with the plant uptake and nutrient needs. For a more modern approach, the PPS Perpetual Preservation System should also be considered as an alternative method towards plant nutrition.