Its dust from the alphagrog, it will settle out or get caught by the filters.
Nice set up by the way.
Add 2 fish to kick start the filter bacteria, feed sparingly then no more fish untill spring. Dont add any filter start you dont need it and besides its made of dead bacteria so doesnt work anyway.
Did you also buy water testing kits? If so test the water every 3 days untill the nitrogen settles down, if it spikes too high then 10% water change imediately.
If you havent bought water test kits go get some.
Nice to see another fish keeper on here.