Your alkalinity is good for fertilizer to work. Go very slow with the 0-40-0 application and put it on platforms etc. (not on the dirt). I would start with only 5 lbs total split in 2 locations. Watch water clarity carefully. If after 2 weeks, you see no change in clarity add 5 more lbs. Until you know how your water reacts go very slowly with fertilization. Just because you can't see the changes does not mean that plankton #s have not increased dramatically.