I use pipe tape for my plumbing and haven't had any issues. I have read though that silicone is the thing to use. But then again I have read that if you use silicone and have to break your tank down and set it back up its apparently a pita to completely remove the old silicone.
If you take a better photo so we can see how your plumbing is put together and maybe you describe it a lil you can prob get some more definitive advise.
Also I think you might have to lower your water level and clean/dry the pieces before you apply anything in order to get a nice seal. I got some silicone from h.d. and the package said that for water immerson it should dry for 48 hours
hth good luck
