I just prchased a 20 G long and want to use an Aqua clear HOB filter. It will be a planted tank with substrate from aquarium plant .com. What size filter should I get? I already purchased a 20, but it looks too small. would a 30 be better? I'm also looking at T5 lights 2x24 watts, one 10,000k the other 6500k. would that be o.k. I could return the small filter, as I have not used it yet. I want to use excel instead of dosing CO2.