Diatoms, brown algae source

I want to know why i get a diatom bloom every time I clean my sand bed. I thought cleaning the sand bed would help PREVENT any sort of diatoms or algae blooms. I do 10 Gallon water change on my 6 month 75 gallon reef tank every other week. When I leave the sand bed untouched or do not blow off my rocks everything is Ok. The times I do the extra work of exporting detritus off my rocks and sand bed my tank looks awful for a few days afterward. Could it be that my sand still has a lot of silicates in the bottom of the sand and i stir it up? If so, should i be more aggressive with the sand bed and eventually the silicates will be removed?

1.024 salinity
0 nitrates
0 phosphates
410 calcium
9 alk
1050 mag.
7.9 ph

I run GFO, carbon and have kalkwasser in my ATO water.
Thanks