I have a 10 gallon 20" long tank that I am trying to get lighting for. I am having a lot of frustration trying to figure out which fixture is best for my tank if I want to grow high light plants like HC/Glosso. Does Finnex have a 20" version? I couldn't find one on the site.... So I am not sure whether to buy the 18" or 24" version, mainly because Im scared that the 18 in wont provide enough light.