-It take a lot of space in the tank
-look dirty on the glass with all sort of color from green black brown.......
-I realy can't have the flow I want or it made sandstorm and dig hole everywere
-My 10 years old blue damesel play all daylong diging in the sand and splach it everywere on coral (I can't get rid of him he is the first fish I cycle the tank 10 years ago and It'a love story between him and me
)
-I have to be realy more carefull when I clean the glass to not scrach it in the bottom
those are the main one It's not big drawback but enought to ask my self why in the world I have put money,and time in this. At least it give me experience