Right, lots of stuff here, so let's get started. First, the light.
Two tubes over an 18g is a lot of light. The natural sunshine will be good with the 6700K tube you have, so replace the 10000K with the sunshine and see what it looks like. Plants will like this combo, but the appearance is another aspect; I think the balance will be pretty good, and your colour rendition of fish and plants should be good as your combination is very close to mid-day sun.
As for the brightness of the two tubes, shading the tank with floating plants is the easiest way to handle this. Another method is to use a non-clear glass between the light and the tank. You want adequate intensity but not more than adequate, both for the fish (they will be brighter coloured and more at ease with less light) and the plants because more intense light means more nutrients to balance and algae finds it easier to take hold if there is more light than the plants can use.
Now to the plant questions. The stripe plant is not aquatic, is sounds like a species of Dracaena, commonly sold in pet stores as an aquarium plant, but placed under water it will (if lucky) last a few months then rot. Forget it. Rotting plants cause more troubles.
If the plant that lost its leaves is a crypt, leave it; this is called a melt. Crypts are very prone to melting when they are moved (sometimes even within the same tank so don't move crypts unless absolutely necessary) or if water parameters or quality changes enough they will melt. Usually the roots remain alive, and new leaves will appear sometimes within days, sometimes weeks; I read of one crypt that came back after a year.
Pygmy chain sword (Echinodorus tenellus) is a lovely plant; you can read about it in our plant profiles section. Just get one, it will quickly send out runners through or on the surface of the substrate and daughter plants will spring up. You can easily cut these off when they get more than you want. A very nice plant, I have it in both my Amazon tanks; the present 90g flooded Amazon forest has Echinodorus tenellus as the foreground plant, and in the 115g Amazonian riverscape it is E. quadricostatus (I think) on the right side, slightly longer and wider leaves than E. tenellus; both are chain swords, E. tenellus is the more commonly available.
Java Moss is lovely; it is used on wood and rock, so if you have a piece of wood or some rock in the tank, stick a piece of
Java Moss on it (you can use thread, or just wedge it between the wood/rock and substrate) and it will grow and attach itself to the wood or rock. It is easy to pull bits off when there is more than you want. A nice plant for adding dark green on the bottom level of the tank, and fish like it for spawning and feeding (bits of food in the Moss). I encourage this to grow on my bogwood.
Last on the ferts. I have previously tried repeatedly to find out what exactly is in the Tetra PlantaMin without success. I am wary of anything that won't tell you just what "nutrients" it contains.
Kent Pro-Plant is described a bit here
http://www.petmeister.com/item2505.htm and it indicates that other products are needed to supply the missing iron, etc. I used to use the Kent "Freshwater Plant" it is called, and it was good. If your store carries Kent products, they might have the Freshwater Plant and I can recommend that. But I am not so sure about Pro-Plant.
Byron.
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