If your Riccia is dying you could need better lighting.What is you kelvins level. Plants will grow well under 65k and 67k. Both will do great for growing plants and are really cheap.You can buy at any Home supply store for like 10-12 bucks for 2. UV isnt really nessesary,actually they are doin research on wether or not UV has any benefit on PDF's.Hope this helps
