Dave there has been alot of talk around forums about LR leeching phosphates - And the type of rock you put in your tank keeps coming up. Also I was talking with Randy up in knoxvegas - he has been reading about phosphates that do not show up on our test kits causing algae. That is just murphys law I guess. We test and test for phosphates and apparently there are some types of phosphates that we cannot or our test kits do not show. He has had 0 readings on his phosphate tests but has a lot of algae growth. I would deffinately run the DI. Good luck with it!!