Yes, I recently noticed that too! I am surprised it's lasting this long! maybe the soil is good for longer than 2 months unlike the package claims lol.
I also noticed that recently (for roughly the past 5 months) I have not had to even clean my glass from algae anymore! It stays very clean now, and plants are growing without algae or other problems. I wonder how long this will last, before the next algae bloom sets in? (my last bloom was a complete take over by cladophora algae which made all my plants fuzzy. it happened roughly 5 months ago.)