I taught it was diatoms let it go for 5 weeks. just kept getting worse. Went without lights for 4 days in hope of killing .Turn lights back on 2 days latter it returned slowly . Vacuumed up all the sand it is on did not help still coming back.its has been 7 weeks now. I read the only way to get rid of it is to rise ph. Do I have to rise with kalk thats a scary thought for a newbie. the tank is a 20gal long with 10 gallon sump. tank has been set up in my house for 5 months. It was a established tank I bought used before that. Went through small cycle when moved to my house.