01-28-2012, 03:42 PM
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First thing to recognize is that plants will grow fine in practically any substrate. They need light (of sufficient intensity and duration) and 17 nutrients in balance with each other and with the light. All nutrients must be contained in the water before the plants can assimilate them either via roots or leaves, and aquatic plants use both to varying degrees.
Laterite is of very limited value in planted tanks. Laterite is simply iron clay, and while iron is important, it is only one micro-nutrient. I did set up my 115g several years ago with laterite, and frankly saw no difference in the plant growth in this tank compared to my other two large tanks without laterite (comparing the identical plant species, and under identical light, and with the same gravel substrates except for the added laterite in the 115g). And yes, it does have to go on the bottom glass, with the gravel or sand above it. It will cloud the water, though that is not the real issue; iron is now known to cause algae, plus it is a heavy metal and highly toxic to all life forms. As if all this wasn't enough, an excess of iron can also cause plants to stop assimilation of some other nutrients.
A caution on using water clarifiers. I don't know what "TheraP" is, but many clarifiers function by causing suspended particulate matter to stick together so the filter will more quickly catch them i the media. Some of these also bind fish's gills and this is highly stressful at the least and may kill the fish.
Back to your substrate. Provided it is comprised of suitable sized particles, and of sufficient depth for the plant species, it will be fine. But nutrients may be lacking (the yellowing leaves indicate this, provided the light is sufficient) and can be added via liquid fertilizers or substrate tab fertilizers. We can discuss this more once we know the plant species, light specs, and current fertilizers being added.
Last edited by Byron; 01-28-2012 at 03:46 PM..