Oi!
Odd that you mentioned a blue sponge, of all the sponges we can get in our tanks, the blues are actually the most toxic of sponges that are considered toxic.
In Dr. R. Schmiks new book 'reef inverterbrates', although when I talk with him at IMAC this year I have many many questions about his comments about [bad] critters, and how I believe that some of his comments are slanted to the ACROPORITES ideas about starving everything in the tanks; he mentions that all 'bought' sponges are toxic to the tanks even if they are good working order, but I have read in many other books that the blues are the most unperdictable when it comes to releasing toxins into the tank.
So this brings another view into this discussion, go with the idea about the use of some carbon in the filters somewhere [and another thing about carbon, you know {and if you don'rt here is some good advice} that the carbon is only active for about 3 or 4 days at the most for 'toxin' and 'chemical' removal, that's it, no more and probably less depending on the amount of carbon and the amount of water flowing over it; The fact that we leave it in for so long {a month or more} is that even though it is no longer removing the 'chemicals' out of the water, it is now truning into a biological filter with the 'gunk' growing on it, also very benificial, which is why we leave the old in for as long as we do, but it's the biological benifits after it has spent it's ability to remove the 'chemmical'] and if you want to see if it is a 'chemical' thingy then remove the carbon after a few days and replace it [no I'm not selling carbon]. Once you believe that the 'chemicals' are under control, then leave the carbon in and allow the biological filtering to continue.
