i have xp4 and i am going to add wit/dry filer real soon....about 20mnts ago i open the filter and took out the bio-balls out that i put in yesterday when i was cleaning the filter,i remember now that last year i did the same thing by adding bio-balls in the filter and it did the same thing....i a have felling that is what causing my water to be come cloudy....i guess i just have to wait an see...ward1066;3083470; said:from your pic it looks like you have a xp3,, you will at least need 2 full of substrat pro or matrix IMO.