Question: When to clean substrate (and how)

Hey all, i have a CoralLife BioCube 29 that i purchased and started on 5/19/16... Currently there is about 4 inches (2x 20lb bags) of CaribSea Arag-Alive Live Aragonite (granual size step or two above sugar) and 25-30 lbs of man made rock (bacteria coated). Been running for about 3-4 weeks. Have brown algae thats been growing steadily for the last week. I have done 2 25% water changes. I have about 12-15 snails 3 different types (not sure which ones) that i bought from LFS. Other tank mates are 2 Ocellaris Clowns, a Helfrichi Firefish and a Blood shrimp. Now the questions:

When should I clean the substrate? (Was planning on doing tonight with water change)

How often should a substrate cleaning be done? (I am aware that there are beneficial bacteria in there so how much is too much?)

Finally, what is the best method for cleaning / sifting? (I have the standard tube type syphon)

Many different ideas on internet just wanted a more personalized answer.

Thanks in advance for your input!! (Also im sure this topic has been brought up before in this forum, but a search didnt reveal any answers, feel free to direct me to a link)...