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Red clay for the aquarium

     One of the important properties of laterite and other soils used as 
     additives in aquatic substrates is the iron content. I suspect that 
     this is the primary reason that we can observe improved growth rates 
     and plant health in these enriched substrates compared with plain sand 
     or sand only enriched by fish wastes.
     Another important factor in improved plant growth rates, and health is 
     the presence of additional nutrients (in moderation) in the substrate. 
     Excessive amounts of organic material or nutrients will result in high 
     concentrations of nitrates and phosphates in the aquarium water which 
     will encourage many kinds of algaes especially cyanobacteria 
     (blue-green "algae") and various filamentous algaes. Many aquarists 
     prefer to use peat as an additive for its resistance to decomposition 
     and relatively low levels of nutrients.
     One of the negative attributes of clay is that if you are not careful, 
     you can create very cloudy (turbid) water. You should be familiar with 
     the precautions for using clay before you experiment with it.
     The Optimum Aquarium (TOA) book is an excellent reference book 
     describing the use of laterite and provides an easy to follow, highly 
     repeatable methodology for growing aquarium plants. It is of course 
     somewhat oriented towards the Dupla product lines and there are other 
     easy and cheaper methodologies for growing plants. There are many 
     right ways of growing aquatic plants and the right method for you is 
     often a matter of taste and past experience.
     Alternative sources for iron in the substrate include natural red 
     clays, most soils (except sand) and micronized iron which you can find 
     in gardening centers. Other trace nutrients (not found in laterite) 
     are found abundantly in many types of mineral soils including top 
     soil. Of course it is also fairly easy to provide those nutrients from 
     commercial products (eg. Dupla Drops, Tropica Mastergrow, Flourish...) 
     or from the PMDD recipe (discussed in the APD archives endlessly)
     I prefer to provide most of my plant nutrients from the substrate 
     since it reduces my reliance upon regular dosing and frequent nutrient 
     concentration testing. You still need to provide Ca, Mg and K in the 
     water. It is often advantageous to supplement chelated Fe to some 
     degree in the water particularly with new or relatively shallow 
     substrates. Crypts may be adept at getting Fe from the substrate but I 
     don't think all plants do as well although almost all rooted plants 
     benefit greatly from iron, fine materials (silt, clay) and somewhat 
     higher nutrient levels in the substrate.
     A forthcoming article in TAG on the subject of substrates by yours 
     truly should be coming out real soon now. If Neil Frank is currently 
     following the APD I hope he can give us an update since many of us in 
     the AGA are pining for our next issue of TAG! ;-)
     Steve Pushak in Vancouver where the summer weather is just glorious