Are you using or did you use 2 different types of white sand? I did & saw something similar to what’s here. I think that’s green algae mixed with the sand. I vacuum it out & wipe down tank interior with a white magic eraser sponge. I also remove & rinse off decorations periodically. Yours look clean, but mine had green algae on them.View attachment 148867
Any idea what this could be? Is it just a case of dirty sand? And any tips to clean it. Thanks