aquatic plants usually do better out of water in a moist environment because they get co2 in a much more concentrated level. Riccia kinda does both and grows as a floating plant most of the time. DIY co2 reactors will lower your ph not increase it, but not substantially at all. In fact, the more co2, light, and available minerals there are, the faster riccia will grow. If you do decide to grow it in an aquarium, seachem flourish is a great brand of liquid fertilizer. I would recommend using comprehensive, iron, and potassium for maximum growth. Just remember that plants need NPK and M which stands for nitrogen, phosphorous, potassium, and micronutrients (like iron, magnesium, calcium, etc...) Seachem flourish excel can also be used as a replacement for the diy co2 reactor, because it basically does the same thing. Aquatic plant central is a good site to get your feet wet with aquatic plants (no pun intended). Good luck!