I have a 20 gallon freshwater planted tank. I have a finnex ray 2 led light, a Marineland filter, a small uv sterilizer light in the filter, and now a diy c02 diffuser. I have jungle vals in it and I just added the c02 but I am unable to keep them alive it seems. I just bought flourish excel but it's in the mail shipping. I have black gravel ad substrate. I am desperate to make my plants grow. Is there anything I'm doing wrong? I don't overfeed and I do regular water changes. I have a dwarf gourami, snail, neon tetra, pleco and rainbow fish. Please help me.