You should get a good phosphate test kit I'm assuming because of the numbers you listed it's an api test kit? Putting a blanket on a tank to kill off algae won't decrease phosphates but if anything increase phosphates , think about it if algae dies where does that po4 go? Back to the water colum so right away I'd be looking at my test kit going well thats a bit odd lol get a fresh phosphate test kit when you have the chance next it will make life alot easier in the long run
Also have a read here about phosphates as well check out other articles they have
http://reefkeeping.com/issues/2006-09/rhf/