I always suggest the Finnex lighting. There are different kinds of lighting setups clip on and LED bar type. For the price Finnex Sting Ray Would be the one I would recommend. It is by far the best all around lighting. offering lighting for low to high light for small planted tanks. The bar type is adjustable in length and the 20 inch would fit the 18.1 inch tank with ease. Giving you the light you want with out having to worry about which plants would work with your lighting. Here are two links to Finnex lighting and the Finnex company that sells them.
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I have used Finnex Planted plus in every tank I have for years and each time I get new tanks They are the first place I go to. You would need a glass canopy and that is easy to find on Amazon.