I've been cycling my tank for 3 weeks now and I had my Betta in at first but I took it out because I found out about cycling, I've been doing water changes every week 25% - 50%. I noticed that there's this white fluffy stuff all in the bottom of the tank and my decorations, yes when I do water changes I use gravel vacuum and when I do water changes the white fluffy goes everywhere in the tank I've read that it's normal when cycling but I'm not sure?
here is a picture:

you can see the white fluff on top of it