I really don't think the Stingray is going to provide enough light for what you're trying to accomplish. I ran two 20 highs with 24" Stingrays and they were great low tech tanks but the almost complete lack of any algae suggests to me that they were pushing the mid to lower end of low tech. The Finnex Planted + 24" may just do the trick. You may be getting around 30 PAR at that depth but I'm not 100% on what the actual figures are for the 24" light. There are also a number of other great lights that may suit your needs like the Current Freshwater Plus which should give you a little over 30 PAR and has some really nice features. There's the Fluval Aquasky as well but that's relatively new and concrete information about PAR values is hard to come by.